Anhydrous, amorphous and porous magnesium carbonates and methods of production thereof

ABSTRACT

An X-ray amorphous magnesium carbonate is disclosed that is characterized by a cumulative pore volume of pores with a diameter smaller than 10 nm of at least 0.018 cm 3 /g, and a specific surface areas of at least 60 m 2 /g. The X-ray amorphous magnesium carbonate is produced by reacting an inorganic magnesium compound with alcohol in a CO 2  atmosphere. The X-ray amorphous magnesium carbonate can be a powder or a pellet and acts as a desiccant in, for example, production of food, chemicals or pharmaceuticals.

RELATED APPLICATION DATA

This application is a U.S. National Phase Application of InternationalApplication No. PCT/IB2013/060647, filed 4 Dec. 2013, which is based onand claims priority to U.S. Provisional Patent Application No.61/734,144, filed Dec. 6, 2012, the entire contents of which areincorporated herein by reference.

FIELD OF INVENTION

The present invention relates to an amorphous, anhydrous, micro porousmagnesium carbonate with large specific surface areas and extraordinarymoisture sorption properties and to a method of forming such. Theinvention further relates to, but is not limited to: dehumidifiers,moisture control, vacuum insulation panel and thermochemical energystorage materials, delivery or carrier systems for therapeutic andcosmetic or volatile agents, odour control, sanitation after fire orfire retardants, as well as to materials for collection of toxic waste,chemicals or oil spill and to materials for pest control and forprotection of crops and food stuff.

BACKGROUND OF THE INVENTION

In the discussion that follows, reference is made to certain structuresand/or methods. However, the following references should not beconstrued as an admission that these structures and/or methodsconstitute prior art. Applicant expressly reserves the right todemonstrate that such structures and/or methods do not qualify as priorart against the present invention.

Magnesium is the eighth most abundant element in the earth's crust andessential to most living species. It can form several forms of hydratedcarbonates such as nesquehonite (MgCO₃.3H₂O), and lansfordite(MgCO₃.5H₂O), a number of basic carbonates such as hydromagnesite(4MgCO₃.Mg(OH)₂.4H₂O), and dypingite (4MgCO₃.Mg(OH)₂.5H₂O) as well asthe anhydrous and rarely encountered magnesite (MgCO₃). The variousforms of magnesium carbonate are all industrially important materialsand for example used in pharmaceutics as antacids, adsorbents anddiluents in direct compression tablets. They are also found in cosmeticsthanks to their mild astringent properties which help to smoothen andsoften skin, and have found their applications in dusting powders, facemasks as well as in toothpastes. In addition, high purity magnesiumcarbonates are useful desiccants, for instance, as an additive in tablesalt to keep it free flowing or as a drying agent for hands to improvethe grip, e.g. for rock climbing, gymnastics, and weight lifting.

Commercial (crystalline) analogues of magnesium carbonates typicallyshow specific surface areas (SSAs) of about 4-18 m² g⁻¹. For previouslyreported X-ray amorphous magnesium carbonates produced by thermaldecomposition of hydrated magnesium carbonates forms, the highest SSAfound in the literature is ˜50 m² g⁻¹.

For many geologists, the anhydrous (native) magnesite is a conspicuousrock with unclear genesis. Although magnesium carbonates are abundant innature in the form of minor traces in most geological structures,magnesium carbonate rarely exists as a monomineralic magnesite ineconomically viable deposits. In fact, there are virtually only twotypes of magnesite deposits in the world: the sparry magnesite ofVietsch type, which constitutes 90% of world's reserves and forms nearlymonomineralic lenses within marine platform sediments, and the lesscommon but highly valued Kraubath type magnesite of superior quality.The Kraubath type consists of veins (300-400 meter deep) and stockworks(80 meter deep) of cryptocrystalline “bone” magnesite, also sometimesreferred to as gel-magnesite. It commonly occurs together withultramafic rock structures such as serpentine ((Mg,Fe)₃Si₂O₅(OH)₄) andolivine ((Mg,Fe)₂SiO₄) minerals. The formation of Kraubath typemagnesite is suggested to occur through a so-calledepigenetic-hydrothermal route, wherein hydrothermal fluids of moderatetemperature and low salinity carrying CO₂ interact with ultramaficrocks. Most of the silica and iron derived from the decomposition ofultramafic rocks are carried to the surface whereas the veins ofmagnesite precipitate in situ as a gel.

In nature, magnesium carbonate occurs in two physical forms; asmacrocrystalline or cryptocrystalline magnesite. The cryptocrystallineform is also sometimes referred to as amorphous or gel magnesite bygeologists, however, it should be stressed that this does not imply thatit is X-ray amorphous, merely that the size of the crystallites are toosmall to be observe with a light microscope. Hereinafter the termamorphous should be interpreted to mean X-ray amorphous.

X-ray amorphous magnesite has been observed upon thermal decompositionof crystalline hydrated magnesium carbonates occurring at temperaturesof the order of 300° C. or higher. Such magnesites are, however, notstable upon long term storage in humid atmosphere as it has been shownthat the carbonate bond is weakened during rehydration. This weakeningis evident by the fact that the decarbonation peak in differentialThermogravimetic measurement (dTGA) curves at about 350° C. or abovedevelops a shoulder and/or splits into two or more peaks and also shiftstowards lower temperatures.

Interestingly, magnesite has stirred problems not only for thegeologists but also for the chemists. Anhydrous MgCO₃ can easily beproduced at elevated temperatures. However, numerous authors, havedescribed unsuccessful attempts to precipitate anhydrous magnesiumcarbonate from a magnesium bicarbonate solution kept at room temperatureand under atmospheric pressure. Instead, hydrated magnesium carbonatesor one of the more complex basic magnesium carbonates precipitated undersuch conditions leading to what has been branded as “the magnesiteproblem”.

In 1999, successful attempts of making crystalline magnesite at 400° C.and atmospheric pressure was presented by using a suspension ofartificial sea-water with calcium carbonate and urea through which CO₂was bubbled followed by dissolution and titration with dilute ammoniaduring which carbonate precipitated. The precipitate was characterizedas crystalline magnesite using X-ray diffraction, and traces ofaragonite (CaCO₃) and possibly calcite (CaCO₃) were noted in thediffractogram. The experiment has since been repeated and theprecipitates consisted of magnesite with traces of aragonite (CaCO₃) anddypingite (Mg₅(CO₃)₄(OH).5H₂O). In both of the experiments magnesite wasformed after 14 dissolution-precipitation cycles.

It should be mentioned that magnesium carbonate was attempted to besynthesized also in non-aqueous solvents during the early 1900's.However, it was concluded that magnesium carbonate cannot be obtained bypassing CO₂ gas through methanolic suspensions of MgO due to the morelikely formation of magnesium dimethyl carbonate Mg(OCO)(OCH₃)₂.

Subsequent studies only reiterated the assumption that MgOpreferentially forms complex dimethyl carbonates when reacted with CO₂in methanol. This conclusion was especially peculiar since carbonates ofother rare earth metals, such as those of Ca, Ba, and Sr, can be readilyproduced by passing CO₂ gas through alcoholic suspensions of theirrespective oxides.

In view of the above-mentioned industrial applications of magnesiumcarbonates and their non-toxic properties, further improvements in themagnesium carbonates and their production methods are desirable to allowfor expanded use of magnesium carbonates in various applications. Aswell, introduction of a new class of magnesium carbonate containingmaterials with structural and functional properties that have currentlynot been found in previously disclosed magnesium carbonate containingmaterials are foreseen to open up for new industrial applications andfor improved functionality in already existing applications. To becomeindustrially attractive, areas of improvements include water sorptionproperties, porosity, specific surface area, long term stability of thematerial and the cost of production.

There are, to our knowledge, no prior art disclosing a magnesiumcarbonate material containing micro and/or meso pores, neither among thereports describing crystalline magnesium carbonates nor the X-rayamorphous ones produced by thermal decomposition. A nitrogen sorptionanalysis performed on, e.g., hydromagnesite (Mg₅(CO₃)₄(OH)₂.5H₂O)),which is the pharmaceutical grade of magnesium carbonate, reveals amaterial with no porosity in the micro pore range and with some mesopores between, but not inside, the powder particles, as will becomeevident in the drawings and examples that follows.

Magnesium carbonates are well known for their desiccant properties inapplications like those mentioned above, e.g., for keeping table saltfree flowing in humid climates and as gripping agents in rock climbing.Existing magnesium carbonate majorly adsorbs moisture around or above70% relative humidity (RH) at room temperature and are not know to begood moisture adsorbents at low RHs.

The stability of presently known amorphous and anhydrous magnesiumcarbonates, i.e. those produced by thermal decomposition of crystallinehydrated magnesium carbonates, are known to be limited upon storage inhumid environments. The carbonate bond of such materials usually weakensafter only 2 weeks of storage in 100% humidity, preventing aregeneration of the materials original structure and properties.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel group ofmagnesium carbonate based materials with improved properties withregards to, for example, surface area, micro and meso pore volume,moisture sorption properties and regeneration properties as well asstorage stability as compared to other carbonates as well as to otherclasses of materials used for, e.g., moisture sorption and drugdelivery, as well as other applications exemplified herein. It is afurther object to provide methods of producing such magnesium carbonatebased materials, which are industrially feasible.

Herein micro pores, refers to pores with a diameter less than 10 nm andmeso pores refers to pores with diameters between 10 and 100 nm, insteadof the traditionally used range of 2-50 nm. Accordingly, micro porousrefers to a material comprising micro pores with a diameter less than 10nm and meso porous refers to a material comprising meso pores with adiameter between 10 nm and 100 nm.

Surprisingly, we have found that anhydrous, amorphous, micro porous,high specific surface area magnesium carbonate with unique moisturesorption properties at low RHs can be produced at low temperatures froma Mg-containing precursor, like MgO, in organic solvents. The magnesiumcarbonate produced can be either in the form of suspension, gel orpowder. The produced magnesium carbonate has a surface area much largerthan that reported for any other magnesium carbonate material andcomprises a substantial portion of micro pores, i.e. a cumulative volumeof pores with a diameter smaller than 10 nm in the range 0.018-3 cm³/g.The novel material is stable upon storage at high RHs for prolonged timeperiods, in contrast to earlier described amorphous magnesium carbonatematerials. Further, we have also found that the produced magnesiumcarbonate has excellent moisture sorption properties, especially at lowRHs, which are highly favorable in a number of industrial applications.These and other advantages of the material are described in detailbelow. The introduction of a new class of magnesium carbonate containingmaterials with structural and functional properties that have currentlynot been found in previously disclosed magnesium carbonate containingmaterials are foreseen to open up new industrial applications andimproved functionality in already existing applications.

The magnesium carbonate according to the invention is X-ray amorphous,anhydrous, exhibits a cumulative volume of pores with a diameter smallerthan 10 nm of at least 0.018 cm³/g, preferably of at least 0.4 cm³/g,and even more preferably of at least 0.8 cm³/g, and a cumulative volumeof pores with a diameter smaller than 10 nm up to 1.5 cm³/g, or morepreferably up to 2 cm³/g or most preferably up to 3 cm³/g. Asappreciated by the skilled person, the unique distribution of micro andmeso pores according to the present invention can be described withother parameters and can be based on other types of measurements thandescribed herein.

Such pore volume should be determined by Density Functional Theory (DFT)analysis of nitrogen sorption isotherms, wherein the pore sizedistribution is derived from the nitrogen isotherm using the DFT methodassuming a slit-shaped pore model. The magnesium carbonate according tothe invention further exhibits a specific surface areas (SSAs) of atleast 60 m²/g, preferably of at least 100 m²/g, more preferably of atleast 240 m²/g, even more preferably of at least 350 m²/g, mostpreferably of at least 600 m²/g, and a SSA up to 400 m²/g, preferably upto 800 m²/g, more preferably up to 1000 m²/g, even more preferably up to1200 m²/g and most preferably up to 1500 m²/g. The specific surface areacan be determined from a BET analysis of nitrogen adsorption isotherms.

The method according to the invention of producing the high SSA, porous,amorphous and anhydrous magnesium carbonate, comprises reacting aninorganic magnesium compound, for example MgO, with alcohol in a CO₂atmosphere. The pressure should preferably be 1-3 bar, and thetemperature 40° C. to boiling temperature of the liquid. The method maybe realized by the steps:

[Step 1] Mixing a Mg-containing precursor and an alcohol-containingliquid in a reactor, the mixing is preferable performed under continuousstirring and the consistency of the mixture is preferably of liquidcharacter. During this step, the ingredients in the mixture react toform one or several intermediates that later can interact with CO₂. themixture is preferably heated in order to facilitate reactions betweenthe ingredients in the mixture. Temperatures between 40° C. and boilingtemperature of the liquid are preferable for the reaction to occur,however lower temperatures down to the freezing temperature of theliquid is enough for a less complete reaction. typically about 3 h to 24h at 50° C. for liquid volumes of 100 to 3000 ml. [Step 2] Reacting themixture with CO₂. In this step, the intermediate products formed duringstep 1 interact with CO₂ to form one or several types of carbonatedintermediate products. this step can be performed at temperaturesranging from the freezing temperature to the boiling temperature of theliquid, and at CO₂ pressures ranging from 0.001 to 200bar aboveatmospheric pressure. However, temperatures below 30° C. and pressuresbelow 5bar are beneficial for carbonation of the intermediate products.during this step, the carbonated intermediate products can form a gel inthe reactor, typically this occurs after 4-6 days if the CO₂ pressure is1 bar and the temperature is 20° C. during step 2. [Step 3]Solidification and drying of the material. the liquid or gel formed inthe reactor during step 2 is dried in order to obtain a solid materialand the carbonated intermediate products formed during step 2 aretransformed into anhydrous magnesium carbonate. temperatures between 60°C. and 300° C. depending on the intermediates formed during step 1 and2, presence of water during the step can facilitate the transformationto magnesium carbonate via hydrolysis. the drying and solidificationprocess in may include techniques such as spray drying or oven drying.

Thanks to the present invention it is possible to provide an amorphous,anhydrous, micro porous and high surface area magnesium carbonate whichis stable upon storage for months or longer, at room temperature andrelative humidity at least above 60%. The novel material exhibitextraordinary moisture sorption properties, especially at low RHs, andis comparable, or even superior, to those of hydrophilic zeolites, e.g.zeolite Y (600 m² g⁻¹, silica/alumina ratio 5.2:1) and also superior tothose of commonly used dessicants, e.g. fumed silica (Aerosil) orcrystalline hydromagnesite. As measured using an ASAP 2020 fromMicromeritics equipped with a water vapor source, the novel magnesiumcarbonate material adsorbs more than 0.6 mmol water/g material,preferably more than 0.7 mmol water/g material, even more preferablymore than 1 mmol or 2 mmol water/g material, most preferably more than 3mmol water/g material at an RH of 3% at room temperature. It adsorbsmore than 1.5 mmol water/g material, preferably more than 1.7 mmolwater/g material, even more preferable more than 2 mmol water/gmaterial, most preferably more than 4 or 5 mmol water/g material at anRH of 10% at room temperature and adsorbs more than 10 mmol water/gmaterial, more preferably more than 14 mmol water/g material, mostpreferably more than 20 mmol water/g material at an RH of 90% at roomtemperature. Also the moisture retention ability and regenerationproperties are extraordinary; experiments have verified that the novelmagnesium carbonate material retains more than 80 wt % of the adsorbedmoisture when the RH is lowered from 90% to 5% during a water vapordesorption analysis performed at room temperature. Experiments havefurther verified that the novel magnesium carbonate material retainsmore than 90 wt % of the adsorbed moisture when the RH is lowered from90% to 20% during a water vapor desorption analysis performed at roomtemperature. Additional experiments have shown that the moisturesorption properties of the novel magnesium carbonate material can beregenerated after storing the material at RH higher than 90% RH for atleast 7 days at room temperature by drying the material at only 95° C.during less than 24 hours.

The amorphous, anhydrous, micro porous and high surface area magnesiumcarbonate according to the invention may be provided as a mixture orcomposite with other materials, for example for the purpose of tailoringcertain properties. As appreciated by the skilled person unavoidableimpurities and intermediate products may be present in the finalproduct. The remaining part of the material may be any amorphous orcrystalline, organic or inorganic element or compound. Non limitingexamples of such other material include salts, like calcium carbonates,crystalline magnesium carbonates, sodium chloride, magnesium nitrate,copper sulfate, hydroxyapatite, strontium acetate, zink citrate,hydroxides like magnesium hydroxide, strontium hydroxide and siliconhydroxide, oxides like magnesium oxide, iron oxide, silicon dioxide,aluminum oxide, aluminosilicate, metals like gold, silver, zink,aluminum, as well as organic compounds like cellulose, spider silk andsynthetic polymers.

According to one aspect of the present invention the magnesium carbonateof the present invention is produced and used as a functional materialin dehumidification procedures. A non-limiting example of suchdehumidification procedures includes sorption dehumidification todehumidify the air in a so-called drum dehumidifier. In such processes,the humid air may enter through a rotor containing the magnesiumcarbonate of the present invention or a composite thereof that acts as adesiccant in the dehumidifier, and exits as a dry air. The magnesiumcarbonate of the present invention or a composite thereof can also befixed on a porous matrix in the rotor in order to increase the airflowthrough the rotor; this porous matrix can for example be produced frompaper. To regenerate the material, warm (e.g. temperatures between 70and 300° C.) air is blown through a part of the rotor.

According to a further aspect of the invention the magnesium carbonateof the present invention or composites thereof is used as dehumidifyingagent for organic solvents. The solvents may be selected from but arenot limited to acetone, acetonitrile, benzol, chloroform, cyclohexane,diethylether, dichlormethane, diisopropylether, dimethylformamide,dioxane, ethylesther of acetic acid, methylesther of acetic acid,ethanol, n-hexane, methanol, isopropanol, pyridine, tetrahydrofurane,toluol, xylol.

According to a yet another aspect of the invention magnesium carbonateof the present invention or composites thereof is used as anti-cakingagents to keep powders free flowing in production lines and in productsunder moist conditions. The magnesium carbonate of the present inventionor composites thereof renders its action by dehumidification of thepowder bed. Typical examples include, but are not limited to, productionlines in food, pharmaceutical and polymer industries, as well asproducts such as table salt and flour.

According to a yet another aspect of the invention magnesium carbonateof the present invention or non-toxic composites thereof is used as apharmaceutical additive to improve the powder flow during tableting.

According to a yet another aspect of the invention the magnesiumcarbonate of the present invention or non-toxic composites thereof isused as a porous pharmaceutical carrier for active pharmaceuticalingredients. The carrier is particularly useful to improve the apparentsolubility of poorly soluble Type II and Type IV drugs according to BSCclassification. The material of the present invention may also be usedas a pharmaceutical additive which protects moisture-sensitive drugsfrom degrading.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof in pharmaceutical formulations as an excipient in order toprotect moisture sensitive substances from contact with moisture. Themagnesium carbonate will act as a moisture sink in the formulation andadsorb moisture present in the formulation.

One aspect of the present invention includes the production and use ofthe magnesium carbonate of the present invention or composites thereofas a material which is useful as a hand drying agent and a materialimproving the grip for sports and recreation, including weight liftingand climbing.

Yet another aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof as a material for drying packages, containers, cargo etc. duringtransportation and storage.

Another aspect of the present invention includes the production and useof the magnesium carbonate of the present invention or compositesthereof as porous filler material in vacuum insulation panels used forthermal and/or acoustic insulation.

Another aspect of the present invention includes the production and useof the magnesium carbonate of the present invention or compositesthereof in thermochemical energy storage device which utilizes theenergy released due to water vapor adsorption. Such thermochemicalenergy storage is particularly useful in electric appliances including,but not limited to, dishwashers, refrigerators and climate controlequipment.

In an additional aspect of the present invention the magnesium carbonateof the present invention or composites thereof are produced and used inagriculture applications. A non-limiting example of such applicationsincludes the use of the magnesium carbonate of the present invention orcomposites thereof as a carrier of essential oils for pest control. Theinsect or bug repellant oils are stabilized and slowly released from theporous carriers in order to achieve a long-term repellant effect.

Another aspect of the present invention includes the production and useof the magnesium carbonate of the present invention or compositesthereof to protect crops, and other types of food stuff, in bulkstorages against insects, bugs and other unwanted organisms by utilizingthe dehumidifying action of the magnesium carbonate of the presentinvention. The insects, bugs, pest and other unwanted organisms areselected from but not limited to beetles, flies, weevils, worms, moths,mold and cockroaches.

Yet another aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof to expelling insects, bug and other unwanted organisms fromhouses, buildings and storage rooms/containers by utilizing thedehumidifying action of the magnesium carbonate of the presentinvention.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof is in microbial and probiotic formulations preventing moistureto affect the active components in the formulations. By acting as amoisture sink, the magnesium carbonate can stabilize the formulation,minimize the amount of available moisture that can affect the activecomponents, and hinder degradation of the same.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof as an oil, fat or sweat adsorbing agent in cosmetics andcosmeceuticals included but not limited to dry shampoos, face and bodypowders, formulations to treat or prevent acne, formulations for eczemaprone skin. Herein and below the term cosmeceutical refers to thecombination of cosmetics and pharmaceuticals. Cosmeceuticals are, thus,cosmetic products with biologically active ingredients purporting tohave medical or drug-like benefits.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof for delivery of moisture, oil or fat to skin when the materialis used in skin moisturizer products.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof as a cleansing agent that adsorbs impurities from the skin, aswell as acts as an astringent and helps to close pores.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof for delivery of fragrances where the magnesium carbonate of thepresent invention or composites thereof acts as a carrier for thefragrances. Typical applications are selected from but not limited tocosmetics, perfumes, skin-care products and products for odour controlin domestic environments, cars, warehouses, industry buildings, wastedisposal sites, sewage plants and public toilets.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof to improve the ability for cosmetic products to take upmoisture.

Yet another aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof for air sanitation through uptake/adsorption of moleculescausing undesired smells where the magnesium carbonate of the presentinvention or composites thereof acts as an adsorbent for the airbornemolecules. The adsorbing material can be used in air filter systems oras stand-alone adsorbents. Typical applications are selected from butnot limited to domestic odour control as well as odour control in cars,warehouses, industry buildings, waste disposal sites, sewage plants andpublic toilets. The amorphous and anhydrous magnesium carbonate rendersits action through adsorbtion of vapors.

One additional aspect of the present invention includes the productionand use of the magnesium carbonate of the present invention orcomposites thereof for air sanitation preventing or treating yeastdamage of living spaces and commercial facilities by adsorbing geosminand dehumidifying air to prevent yeast proliferation.

One additional aspect of the present invention includes the productionand use of the magnesium carbonate of the present invention orcomposites thereof for air sanitation following fire damage.

One additional aspect of the present invention includes the productionand use of the magnesium carbonate of the present invention orcomposites thereof as a fire retardant.

One additional aspect of the present invention includes the productionand use of the magnesium carbonate of the present invention orcomposites thereof as a biomaterial in applications including but notlimited to: bone void fillers, depot drug delivery systems and deliveryvehicles for local release of therapeutic agents, as well as bone andcartilage repair materials.

One additional aspect of the present invention includes the productionand use of the magnesium carbonate of the present invention orcomposites thereof for collection of toxic waste where the magnesiumcarbonate of the present invention or composites thereof is used as anadsorbent. In such applications, the material may be spread out over thetoxic liquid, which subsequently is adsorbed into the material. Aftercomplete adsorption of the toxins, the material can be removed anddiscarded.

In an additional aspect of the present invention the magnesium carbonateof the present invention or composites thereof are produced and used forcollection of oil spill. In such applications, the material may bespread out over the oil and the material adsorbs the oil. After completeadsorption of the oil, the material can be removed and the oil can beretrieved from the material elsewhere.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof in peeling or polishing applications. Non-limited examples ofsuch applications include peeling creams, lotions, solutions and thelike for face and body as well as tooth pastes and other dentalformulations with polishing properties. In such applications themagnesium carbonate of the present invention may optionally be loadedwith a functional agent improving the action of the peeling or polishingapplication. Non-limiting examples of such agents include flour,whitening agents, vitamins, retinoic acid, trichloroacetic acid, phenol,alpha hydroxy acids like, e.g., glycolic acid, fruit acids like, e.g.,citric acid, glycolic acid, lactic acid, malic acid and tartaric acid,beta hydroxy acids like, e.g., salicylic acid.

A further aspect of the present invention includes the production anduse of the magnesium carbonate of the present invention or compositesthereof is the use of the magnesium carbonate to alter the viscosity andconsistency of ink.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to thedrawing figures, wherein:

FIG. 1. is a graph illustrating the XRD diffraction pattern for amagnesium carbonate of the present invention, wherein the halo at 2θ˜30°indicates the presence of at least one amorphous phase and the sharppeaks belong to crystalline MgO;

FIG. 2. is a graph illustrating the Raman spectrum for a magnesiumcarbonate of the present invention, wherein the peak at ˜1100 cm⁻¹ isfrom the carbonate group and the broad halo with centrum at 100 cm⁻¹ isa Boson peak;

FIG. 3. is a graph illustrating the TGA and dTGA/DTA curves for amagnesium carbonate of the present invention, illustrating how thedecomposition at 390° C. pertains to MgCO₃ and the decomposition priorto that (i.e. observed at lower temperatures) is due to the loss ofremaining organic groups;

FIG. 4. is a graph illustrating the dTGA curves for a magnesiumcarbonate of the present invention, wherein the sample has been storedat 100% humidity and room temperature for the displayed time periods andno visible change in the peak position for the peak at approximately440° C. can be seen;

FIG. 5. is a graph illustrating the water sorption isotherms at roomtemperature for a magnesium carbonate of the present invention (namedUpsalite in the figure), Mg₅(CO₃)₄(OH)₂.4H₂O, Aerosil and Zeolit Y;

FIG. 6. is a graph illustrating the nitrogen sorption isotherm for amagnesium carbonate of the present invention;

FIG. 7. is a graph illustrating the nitrogen sorption isotherm forhydromagnesite (Mg₅(CO₃)₄(OH)₂.5H₂O);

FIG. 8. is a graph illustrating the DFT-based pore size distribution fora magnesium carbonate of the present invention, wherein the pore sizedistribution has a maximum around 3 nm and the cumulative pore sizedistribution gives that 98% of the pore volume is constituted of poreswith a diameter smaller than 6 nm;

FIG. 9. is a graph illustrating the XPS O_(1s) peak for a magnesiumcarbonate of the present invention, wherein the peak at 533.5 eV belongsto MgCO₃ (solid squares in curve fit), the peak at 531.0 eV belongs toMgO (solid circles in curve fit) and the peak at 535.6 eV belongs tosurface adsorbed water (open triangles in curve fit; (the solid linesrepresent the recorded spectrum; open squares represent the subtractedbackground;

FIG. 10. is a graph illustrating the FTIR spectrum for a magnesiumcarbonate of the present invention, wherein the three visible bands(1440 cm⁻¹, 1100 cm⁻¹ and 650 cm⁻¹) are all due vibrations of thecarbonate group;

FIG. 11. is a graph illustrating the XPS Mg_(2p) peak for a magnesiumcarbonate of the present invention, wherein the peak at 52.1 eV belongsto MgCO₃ (solid circles in curve fit) and the solid line represents therecorded spectrum and the open squares represent the subtractedbackground;

FIG. 12. is a SEM image of a magnesium carbonate of the presentinvention;

FIG. 13. is a graph illustrating the nitrogen sorption isotherm of amagnesium carbonate of the present invention in which the synthesizedpowder was heat-treated at 70° C. for 7 days (example 2);

FIG. 14. is a graph illustrating the DFT-based pore size distributionfor a magnesium carbonate of the present invention in which thesynthesized powder was heat-treated at 70° C. for 7 days (example 2);

FIG. 15. Is a SEM image of a spray-dried magnesium carbonate of thepresent invention;

FIG. 16. is a graph illustrating the water sorption isotherm at roomtemperature for a spray-dried magnesium carbonate of the presentinvention;

FIG. 17. is a graph illustrating the DFT-based pore size distribution ofspray-dried magnesium carbonate of the present invention;

FIG. 18. is a graph illustrating the Nitrogen sorption isotherm for aspray-dried a magnesium carbonate of the present invention;

FIG. 19. is a graph illustrating the DFT-based pore size distributionfor a magnesium carbonate of the present invention (example 4);

FIG. 20. is a graph illustrating the weight increase for the magnesiumcarbonate according to example 3 when stored in a sealed vesselsaturated with water vapor at different time periods, at roomtemperature;

FIG. 21. is a graph illustrating the DFT-based pore size distributionfor the magnesium carbonate of the present invention as prepared inexample 5;

FIG. 22. is a graph illustrating the DFT-based pore size distributionfor the magnesium carbonate of the present invention as prepared inexample 6;

FIG. 23. is a graph illustrating the DFT-based pore size distributionfor the magnesium carbonate of the present invention as prepared inexample 7;

FIG. 24. is a graph illustrating the DFT-based pore size distributionfor the magnesium carbonate of the present invention as prepared inexample 8;

FIG. 25. is a graph illustrating the DFT-based pore size distributionfor the magnesium carbonate of the present invention as prepared inexample 10;

FIG. 26. is a graph illustrating the nitrogen sorption of the magnesiumcarbonate material as prepared in example 15;

FIG. 27. is a graph illustrating the DFT-based pore size distributionfor the magnesium carbonate material as prepared in example 15;

FIG. 28. is a graph illustrating the moisture adsorption of themagnesium carbonate material as prepared in example 15;

FIG. 29. Illustrates the X-ray diffraction pattern for the material asprepared in example 24, wherein the peaks correspond to crystallinenesquehonite;

FIG. 30. is a graph illustrating the EGA data for a representativesample of the magnesium carbonate according to the invention;

FIG. 31. is a graph illustrating the growth in pore size associated withdecomposition of organic groups and evolution of H₂O, CO₂ and H₂ fromthe magnesium carbonate according to the invention;

FIG. 32. is a graph illustrating the IR spectrum for the material asprepared in example 26;

FIG. 33. is a graph illustrating the regeneration temperature needed toremove adsorbed water from the magnesium carbonate as prepared inexample 27 as compared to Zeolite;

FIG. 34. is a graph illustrating the pore size distribution (incrementalpore volume in a.u.) obtained from the N₂ sorption analysis of isothermsrecorded on the calcined magnesium carbonate material as prepared inexample 28 (curve with open circles) as well as on the ibuprofen loadedMGCO3-IBU sample (curve with solid triangles) of the same example;

FIG. 35. is a graph illustrating the dissolution profile of freeibuprofen (dashed lower curve) and ibuprofen incorporated in themagnesium carbonate as prepared in example 28 (solid upper curve)recorded at pH 6.8;

FIG. 36. is a graph illustrating the water sorption isotherms at roomtemperature for a calcined magnesium carbonate of the present inventionas prepared in example 29.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a novel anhydrous, amorphous, microporous, high specific surface area magnesium carbonate withextraordinary moisture sorption properties. As is described in detailherein, the material is suitable for use in a wide variety ofapplications.

The novel anhydrous, amorphous, micro porous, high specific surface area(between 60 and 1500 m²/g) magnesium carbonate according to theinvention may be provided as a mixture or composite with othermaterials, for example for the purpose of tailoring certain properties.As appreciated by the skilled person unavoidable impurities andintermediate products may be present in the final product. The remainingpart of the material may be any amorphous or crystalline, organic orinorganic element or compound. Non limiting examples of such othermaterial include salts, like calcium carbonates, crystalline magnesiumcarbonates, sodium chloride, magnesium nitrate, copper sulfate,hydroxyapatite, strontium acetate, zink citrate, hydroxides likemagnesium hydroxide, strontium hydroxide and silicon hydroxide, oxideslike magnesium oxide, iron oxide, silicon dioxide, aluminum oxide,aluminosilicate, metals like gold, silver, zink, aluminum, as well asorganic compounds like cellulose, spider silk and synthetic polymers.

Different suitable methods may be employed, individually or combined, toconfirm and quantify the amorphous magnesium carbonate content of thematerial. These methods can include, but are not limited to, XPS (x-rayphotoelectron spectroscopy), Raman spectroscopy, XRD (x-raydiffraction), FTIR (Fourier transform infrared spectroscopy), NMRspectroscopy (nuclear magnetic resonance spectroscopy), ICP-MS(inductively coupled plasma mass spectrometry), EDS (energy-dispersiveX-ray spectroscopy), TEM (transmission electron microscopy) ED (electrondiffraction) and TGA (Thermogravimetric analysis). As described inExample 1 below, Raman spectroscopy may be employed to reveal thepresence of amorphous magnesium carbonate in the material (by thepresence of the so called Boson peak at low wavenumbers which ischaracteristic for amorphous materials, and the distinctive carbonatepeak at ˜1100 cm⁻¹). To confirm the presence and determine the amount ofmagnesium carbonate in a material, XPS analysis can be employed in thefollowing manner: The magnesium carbonate content in the material can bedetermined by elemental analysis using XPS, and energy resolved spectrumanalysis using the same technique can be used to distinguish betweencrystalline and amorphous magnesium carbonate: the electron bindingenergy in the Mg 2s orbital of amorphous magnesium carbonate is expectedto be ˜90.7 eV while the binding energy generally is expected to be˜91.5 eV or higher for crystalline magnesium carbonates. The presence ofstructural water, i.e. hydrated magnesium carbonates, can be elucidatedvia energy resolved XPS analysis of the O1s peak as described in one ofthe embodiments below. Other techniques can involve XRD analysis forcrystal phase determination of the constituents of a material where theamorphous magnesium carbonate content can be quantified in relation tothe crystalline content.

In particular, the presence of amorphous magnesium carbonate can beconfirmed by XRD. In an XRD measurement amorphous magnesium carbonategives rise to either broad halos or just noisy flat signals in the 20window between about 10° and 20° as well as between about 25° and 40°when the diffractometer uses CuKα radiation. Example of such halos canbe seen in FIG. 1. When the remaining part of a material, consisting ofmaterials other than amorphous magnesium carbonate (including impuritiesor other elements introduced on purpose), such materials will give riseto peaks in the XRD pattern, as also exemplified in Example 1, and seenin FIG. 1, provided that they are crystalline.

The amorphous magnesium carbonate according to the present invention isanhydrous. Anhydrous in this respect means that no structural water isassociated with the bulk of the material, however water molecules areallowed to be tightly or loosely bound to the surface of the material.In this context, tightly bound water does not imply non-regenerablewater (details concerning regenerating moisture sorption ability theamorphous magnesium carbonate of the present invention are describedbelow). Absence of structural water can be verified using X-rayphotoelectron spectroscopy (XPS) following sputter cleaning of thesurface under vacuum as exemplified in FIG. 9. The lack of structuralwater in the bulk is verified by energy resolved analysis of the O1speak: a properly calibrated O1s spectra should contain a peak at ˜533.5eV corresponding to MgCO₃, however no peak component corresponding toH₂O or OH-groups should be present in the spectrum other than that forsurface adsorbed water which is expected around 535.6 eV.

The magnesium carbonate according to the present invention has acumulative pore volume of pores with a diameter smaller than 10 nm of atleast 0.018 cm³/g, preferably above 0.4 cm³/g, preferably above 0.6cm³/g or even more preferably above 0.8 cm³/g, and a cumulative porevolume of pores with a diameter smaller than 10 nm up to 1.5 cm³/g, ormore preferably up to 2 cm³/g or most preferably up to 3 cm³/g which isillustrated in FIGS. 8, 14, 17, 19, 21, 22, 23, 24 and 25.

The pore size distribution and the cumulative pore volume specified inthe above embodiments may be determined by density functional theory(DFT) calculations on the adsorption isotherm with appropriateassumptions about pore shape as exemplified in FIGS. 8, 14, 17, 19, 21,22, 23, 24 and 25.

The combination of amorphicity and presence of micro pores in theamorphous magnesium carbonate of the present invention, as specified inthe above embodiments, is considered to be important for the moisturesorption properties of the material. As is obvious from FIGS. 5 and 16the amorphous magnesium carbonate of the present invention has adramatically higher moisture sorption ability at low and intermediate RHas compared to for example the pharmaceutical grade of magnesiumcarbonate (crystalline hydromagnesite, see FIG. 5) and an amorphousmagnesium carbonate that has a volume of pores with a diameter smallerthan 10 nm below 0.018 cm³/g, see FIG. 28.

The amorphous magnesium carbonate according to the present invention,features a specific surface area of at least 60 m²/g, preferably of atleast 100 m²/g, more preferably of at least 240 m²/g, even morepreferably of at least 350 m²/g, most preferably of at least 600 m²/g,and a SSA up to 400 m²/g, preferably up to 800 m²/g, more preferably upto 1000 m²/g, even more preferably up to 1200 m²/g and most preferablyup to 1500 m²/g.

The specific surface area can be determined by employing the BET methodto nitrogen adsorption isotherms like those presented in FIGS. 6 and 13.More precisely a multipoint BET analysis is performed on the relativepressure range between 0.05 and 0.3 of the adsorption branch of anitrogen isotherm performed at boiling nitrogen temperature. If the BETequation does not yield a linear slope in this pressure range, the BETanalysis should be employed on a more narrow pressure range for accurateresult. The nitrogen adsorption analysis can be performed on an ASAP2020 from Micromeritics after drying the sample at 70° C. for 2 days.Prior to analysis, the sample tube containing the sample is evacuatedwith a vacuum set point at 10 μm Hg and heated to at 95° C. for 10 hwith a ramping rate of 1° C./min. It should be noted that in the caseswhen the specific surface area of the amorphous magnesium carbonate ofthe present invention are of the order of 500 m²/g or larger it iscomparable to that of the exclusive class of high surface area materialssuch as zeolites, mesoporous silicas, metal organic framework materials,and carbon nanotubes.

A large surface area, i.e. larger than the surface area of a macroscopicsolid material, is beneficial for all industrial applications wheresurface interactions are of importance, including but not limited todrug delivery, catalysis, adsorption of various gases and liquids. Itcan be appreciated by one skilled in the art that being able to producean amorphous magnesium carbonate according to the present invention ofhigh surface area will improve the functionality of the material in arange of applications like those mentioned in the summary of invention.

To one skilled in the art it is obvious that the surface area of anymaterial can be increased by diminishing the particle size of saidmaterial. A diminished particle size may also increase the amorphicityof a material as measured by XRD. Large surface areas and amorphicitystemming only from such diminishing of the particle size is generallynot expected to lead to improved properties in applications of magnesiumcarbonates in the applications mentioned above and in the examples aswell as in other application.

With reference to the above; in one specific embodiment of the presentinvention the amorphous magnesium carbonate of the present inventionwith the surface areas detailed above, consists of particles having anequivalent to a sphere diameter of not smaller than 37 nm for more than1% of their number size distribution.

Another way of assessing the presence of micro pores in the material ofthe present invention and also assessing a large surface area is by adirect study of nitrogen sorption isotherms. Thus, according to oneembodiment of the present invention the amorphous magnesium carbonate ofthe invention adsorbs more than 20 cm³ nitrogen/g material at STP at apartial nitrogen pressure of 0.5, preferably more than 25 cm³ nitrogen/gmaterial at STP, even more preferably more than 30 cm³ nitrogen/gmaterial at STP, even more preferably more than 50 cm³ nitrogen/gmaterial at STP, even more preferably more than 100 cm³ nitrogen/gmaterial at STP, even more preferably more than 200 cm³ nitrogen/gmaterial at STP, even more preferably more than 250 cm³ nitrogen/gmaterial at STP during a nitrogen adsorption analysis. The nitrogenadsorption ability is confirmed from gas adsorption experiments likethose exemplified in FIGS. 6 and 13.

The amorphous magnesium carbonate according to the present invention isstable upon storage for up to 13 weeks or longer. Experiments have shownthat the materials can be stable up to 3-5 months and even longer atroom temperature and relative humidities above 20%. In some experimentsthe stability for several months was verified when the material wasstored at 30%, 50, 60%, and also in a sealed humidity cabinet with asaturated water vapor atmosphere. The stability of the magnesiumcarbonate component can be assessed by Differential Thermogravimeticmeasurements (also commonly denoted as DTA or dTGA measurements in theliterature) as exemplified in FIG. 3 and FIG. 4 by observing the peakrelated to the decomposition of the carbonate at above 350° C. Moreprecisely the analysis is performed with a Thermogravimetric analyzerfrom Mettler Toledo, model TGA/SDTA851e. Approximately 15 mg of sampleis placed in an inert aluminum cup and heated from room temperature to700° C. under a flow of air where the temperature ramping rate is 10°C./min during analysis. The stability of the material is confirmed bythe lack of changes in this peak upon storage in a moisture containingatmosphere and also by the fact that the position of the peak is notshifted noticeably (i.e. more than 10-20° C.) towards lowertemperatures. A peak shift towards higher temperatures is however, to betaken as an evidence for stability. Such shifts towards highertemperatures can for example be observed when comparing the experimentsperformed on a dry amorphous magnesium carbonate according to thepresent invention, FIG. 3, with those performed on amorphous magnesiumcarbonate according to the present invention stored for different timeperiods at saturated water vapor, FIG. 4. For an unstable material, onthe other hand, the carbonate decomposition peak at above 350° C. isexpected to develop a shoulder and/or split into two or more peaks andalso to move towards lower temperatures as is the case e.g. for themagnesium carbonate material described in Botha et al. 2003. Thestability of the material of the present invention is industriallyfavorable when it comes to use in e.g. moist environments and ensuresthat the material can be transported, stored and also used at highrelative humidity at prolonged time periods without, due to structuralchanges, losing its functional abilities as disclosed in the presentinvention.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 0.3 mmol water/g material at an RH of 1% at 25° C. Insome experiments it adsorbs more than 0.8 and even more than 1.5 mmolwater/g material. As exemplified in FIG. 5, certain experiments haveshown that the material adsorbs even more than 2.4 mmol water/g materialat this low relative humidity. The water vapor adsorption ability can beconfirmed by first drying the material at 70° C. during at least 48hours and then performing a water vapor sorption experiment as thatexemplified in FIG. 5 and FIG. 16. More specifically this can beperformed with an ASAP 2020 from Micromeritics equipped with a watervapor source. Prior to analysis, the sample tube containing the sampleis evacuated with a vacuum set point at 10 μm Hg and heated to 95° C.for 10 h with a ramping rate of 1° C./min. The measurement is performedat 25° C. starting at low RH with increasing amounts of water vapordosed into the sample tube. The amount of moisture adsorbed on thematerial at a given relative humidity is measured when equilibriumbetween adsorbed and free water vapor is reached in the sample tube.Equilibrium in this case is defined as follows: equilibrium is reachedwhen the pressure change per equilibrium interval (first derivative) isless than 0.01% of the average pressure during the interval. The timeinterval is set to 50 sec during the measurement. In one particularaspect of the embodiment the moisture sorption properties of theamorphous magnesium carbonate of the present invention is comparable, oreven superior, to those of hydrophilic zeolites, e.g. zeolite Y (600m²/g, silica/alumina ratio 5.2:1) and also superior to those of commonlyused desiccants, e.g. fumed silica (Aerosil) or crystallinehydromagnesite. An example of such a material according to the presentinvention is given in FIG. 5.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 0.5 mmol water/g material at an RH of 2% at 25° C.Experiments have shown that the material adsorbs more than 0.8 or evenmore than 2.0 mmol water/g material, while other experiments have shownthat it adsorbs even more than 3.5 mmol water/g material (see e.g. FIG.5). The water vapor sorption ability was confirmed as described above.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 0.6 mmol water/g material at an RH of 5% at 25° C.,and even more than 5.3 mmol water/g material. The water vapor sorptionability was confirmed as described above.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 1.0 mmol water/g material at an RH of 10% at 25° C.and even more than 6.3 mmol water/g material. The water vapor sorptionability was confirmed as described above.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 1.0 mmol water/g material at an RH of 20% at 25° C.and even more than 8.3 mmol water/g material. The water vapor sorptionability was confirmed as described above.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 1.5 mmol water/g material at an RH of 50% at 25° C.and even more than 10.3 mmol water/g material. The water vapor sorptionability was confirmed as described above.

The amorphous magnesium carbonate according to the present inventionadsorbs more than 5.0 mmol water/g material at an RH of 90% at 25° C.and even more than 13.5 mmol water/g material. The water vapor sorptionability was confirmed as described above.

The amorphous magnesium carbonate according to the present inventionretains more than 30 wt % of adsorbed moisture when the RH is loweredfrom 90% to 5% during a water vapor desorption analysis performed at 25°C. as exemplified in FIGS. 5 and 16. Typically the material retains morethan 50 wt % or 60 wt % of the adsorbed moisture and even more than 80wt % of the adsorbed moisture. More precisely the analysis is performedimmediately after a water vapor adsorption analysis as described aboveby lowering the water vapor pressure in the sample tube. The desorptionanalysis is allowed to start once the RH has reached and equilibrated atat least 94% RH in the sample tube. During the desorption study, the RHin the sample tube is lowered stepwise and the amount of desorbed vaporis measured at specified relative humidities. The amount of water vapordesorbed from the material at a given relative humidity is measured whenequilibrium between adsorbed and free water vapor is reached in thesample tube. Equilibrium in this case is defined as follows: equilibriumis reached when the pressure change per equilibrium interval (firstderivative) is less than 0.01% of the average pressure during theinterval. The time interval is set to 50 sec during the measurement.

The amorphous magnesium carbonate according to the present inventionretains more than 40 wt % of adsorbed moisture when the RH is loweredfrom 90% to 20% during a water vapor desorption analysis performed at25° C. as exemplified in FIG. 5 and FIG. 16. The water vapor retentionability was confirmed as described above.

The ability to retain moisture in the structure upon lowering of therelative humidity after moisture sorption as described in the aboveembodiments is a highly favorable property of the material according tothe present invention and rather unique amongst moisture adsorbents asexemplified in FIG. 5. As will be appreciated by one skilled in the art,the fact that the material of the present invention not easily lets goof the moisture adsorbed when a lowering of humidity is performed afteradsorption prevents moisture from being released to the environment fromwhich it was removed by an accidental or purposeful lowering of thesurrounding humidity. As will become clear from below, the fact thatonly minor energy input is needed to release the moisture adsorbed inthe structure to regenerate the moisture sorption properties of thematerial is an additionally beneficial property of the material of thepresent invention since it e.g. opens up for energy efficientregeneration of moisture sorption materials.

The moisture sorption properties of the amorphous magnesium carbonate ofthe present invention can be regenerated after storing the material atRH higher than 90% RH for at least 7 days at room temperature. This canbe performed by drying the material at elevated temperatures at 250° C.or more preferably at 150° C., even more preferably at 110° C., or evenmore preferably at 95° C. or below. A person skilled in the art will beable to determine the time needed to dry the material sufficiently andwill find that a longer drying time is needed for low dryingtemperatures. Applying vacuum to the material during the dryingprocedure will obviously decrease the time needed for removal ofadsorbed water species from the material. When drying, for example, 0.2g of material at 95° C. under vacuum with a vacuum set point of 10 μm Hgthe drying time is typically 5 days or shorter. Experiments have shownthat the drying time can be 2 days and even only 20 h or less.

The fact that the moisture sorption properties of the material of thepresent invention may be regenerated can be confirmed by the fact thatat least one of the moisture sorption properties described above isstill valid (adsorption properties below 1%, 2%, 5% 10, 20 and 50% RHand/or adsorption properties below 90% RH and/or desorption propertiesfrom 90% RH to 5% RH and/or desorption properties from 90% RH to 20%RH).

Theoretical Discussion about the Reaction Mechanism

The amorphous and micro porous magnesium carbonate according to thepresent invention, Mg_(x)CO_(y), wherein x=1-2 and y=3-4, is obtainedupon drying of a reaction product between MgO and CO₂ (mildlypressurized) in methanol. The Mg_(x)CO_(y) material disclosed here isamorphous, and, because it is currently not possible to distinguishbetween several amorphous compositions of MgXO_(y), it includes MgCO₃,MgCO₃.MgO, and Mg₂CO₄, although preferably x=1 and y=3, and any of theircombinations as well as their solvates.

For the sake of simplicity, the basic reaction of magnesium carbonateformation from MgO and CO₂ in alcohol could be condensed into thefollowing terms:MgO+CO₂→MgCO₃2MgO+CO₂→Mg₂CO₄

However, the reaction between solid MgO and gaseous CO₂ does not readilyproceed or is too slow, and one skilled in the art will understand thatin reality the reaction scheme is much more complex and involves severalimportant intermediates which form in the alcohol phase. By consideringthe role of these important intermediates, which will be highlightedbelow, one skilled in the art will also appreciate that the finalproduct, i.e. Mg_(x)CO_(y), could be obtained in many ways, i.e. withoutdirect use of MgO, including metallic Mg or several Mg containinginorganic and organic compounds. Therefore, the reaction scheme proposedherein below should not be perceived in limiting terms.

In the old literature, it has often been considered that oxides ofalkali and alkaline earth metals in alcohols form oxides with alcohol ofcrystallization, i.e. MeO.nROH. The modern understanding though suggeststhat, when dissolved in alcohol, MgO forms alcoholates (also calledalcoxides).MgO+2ROH

Mg(OR)₂+H₂O

Mg(OH)(OR)+ROHThe double-sided arrow above and all other throughout the text should beinterpreted as ⇄, i.e. referring to a reversible reaction.

ROH represents an alcohol which can be any kind of alcohol includingaliphatic, alkenyl, aromatic, primary, secondary, tertiary alcohol aswell as glycol or polyol. Both Mg alcoholate and Mg hydroxyalcoholatecould be formed during the course of the reaction. The fact that thereaction proceeds in the indicated order was confirmed by following theisotopic exchange in the CaO—C₂H₅OH—H₂O system. It has further beendiscussed in the literature that tertiary systems of alkaline earthmetal oxides in alcohol+water can show complex phase diagrams of varyingcompositions which include not only the Me(OR)₂ or Me(OH)(OR).nROH, asexpected from the reaction above, but also Me(OH)₂.nROH. Thus, oneskilled in the art will appreciate that Mg_(x)CO_(y) disclosed hereincould also be obtained from any of the above intermediates byconsidering the appropriate proportions between the components of thetertiary mixtures as well as availability of water in the system and insitu hydrolysis of then-present compounds and their solvates. FTIRanalysis of the samples studied did not reveal the presence ofMg(OH)₂.nROH in the system.

During the development of the magnesium carbonate disclosed herein itwas found that heating the solution of MgO in alcohol, e.g. 50° C.,prior to or during the pressurization with CO₂ was beneficial for highyield of MgOHOCH₃, that currently are considered to be an intermediatein the reaction.

Considering that Mg alcoholates could be important intermediates, oneskilled in the art will further assert that Mg alcoholates could also beobtained using other chemical routes which could include but are notlimited to:

-   -   Reaction of metallic Mg with alcohol;    -   Reaction of Mg(OH)₂ with alcohol;    -   Reaction of Mg amines with alcohol in liquid NH₃ as solvent;    -   Decomposition of Mg hydride, carbide, nitride, amide, sulfide or        organometallic compounds containing Mg;    -   Metatheses of Mg salts with alcoxide of other metals;    -   Metatheses of alcoxides with alcohols leading to a synthesis of        new alcoxides;    -   Oxidation of alkyl derivatives with oxygen;    -   Reduction of carbonyl-containing compounds;    -   Electrochemical reactions in alcohols, e.g. using metallic Mg as        the anode or electrolysis of Mg salts.

Alcoxides of metals are very sensitive to moisture, air, and carbondioxide and behave as “strong base”. They can therefore interact bothwith acids and their anhydrides.

The typical reaction of an alcoxide with acid follows as:

Wherein E=C or S, and X=O or S; and Me=Li, K, Na, Cs, Rb, Mg, Ca, Sr,Ba, Tl.

Upon interaction with CO₂, Mg methylate can form Mg dimethylcarbonate.CH₃.O.C.O.O.Mg.O.CH₃

Mg dimethylcarbonate is similar to Mg hydrocarbonate except that thehydroxyl group is substituted by a methoxy group and thus behavessimilarly with respect to acids and water. It should also be mentionedthat monomethyl hydroxycarbonate salt of Mg have not been described,HO.Mg.O.O.C.O.CH₃which would otherwise be expected to exist considering the structure ofMg dimethylcarbonate. Monomethyl hydroxycarbonate of Mg is deemed animportant intermediate for producing micro- and/or mesoporousMg_(x)CO_(y) disclosed herein.

Another potentially important intermediate is hemicarbonic acid HOCOOR.The importance of the formation of hemicarbonic acid is highlighted byconsidering the possibility of the following reaction:MgO+HOCOOR→HOMgOCOOR

During the development of our material it became clear that pressurizingCO₂ gas (1-12 bar) in the reaction vessel containing MgO in alcohol isimportant, which potentially enables the following reaction:ROH+CO₂

HOCOOR (Pressure)

The formation of hemicarbonic acid in CO₂-alcohol systems has been shownin supercritical fluids at 70-100 bar at 20-40° C. for 2 days byinteracting it with diazodiphenylmethane as a probe to catch acidspecies. These results also showed that in a homologous row of alcoholsthe rate of hemicarbonic acid formation is the fastest for methanol andthe slowest for tert-butanol.

One skilled in the art will also understand that hemicarbonic acid canbe produced by interacting monomethylcarbonate with an acid in anorganic solvent, e.g. dimethyl ether,MeOCOOCH₃+HCl→HOCOOCH₃+MeCl

Thereby, it is also expected that for bivalent Me (e.g. Mg, Ca, Sr, Ba)dimethylcarbonates interacting with water-formed in situ or added instoichiometric quantities-monomethyl hydroxycarbonic salt andhemicarbonic acid could be obtained although no literature reports onthis reaction exist so far.Me(OCOOCH₃)₂+H₂O→HOCOOCH₃+HOMeOCOOCH₃

Alkylesters of hemicarbonic acid are therefore deemed importantintermediates for the formation of Mg_(x)CO_(y) disclosed herein.

Orthocarbonic acid, H₄CO₄, is another possible important intermediatewhich has never been isolated either in the form of free acid or itssalts but only so far is known to exist in the form of esters, i.e.C(OR)₄, or substituted complex ester-salts, e.g. NaCOF₃. However,numerous computational models show that salts of orthocarbonic acid canexist. It should be noted that esters of orthocarbonic acid C(OR)₄ canbe produced from alxocides of Sn, Tl, or Cu. In particular, formonovalent metals Tl, Cu the reaction scheme between alcoxides andcarbondisulfide is the following:4MeOR+CS₂→C(OR)₄+2Me₂S

Considering the similarity between CS₂ and CO₂ as acid anhydrides withsubstituted carbon chalcogenides, the reaction mechanism involvingorthocarbonic acid esters C(OR)₄ and its salts, i.e. COMe₄ (formonovalent metals) and COMe₂ (for bivalent metals), is thereforeplausible yet it has never been proved. It is also expected that if CO₂were used instead of CS₂ the final product should contain some metaloxide in analogy with metal sulfide formed as discussed above.

In all, it infers from above considerations that the mildly pressurizedmixture of MgO, CO₂, and alcohol represents a rather complex cocktail ofdifferent intermediates at equilibrium which can be shifted by changingthe concentration, pressure, and temperature of the system. By usingFTIR-spectroscopy, the following two intermediates were clearlydetectable, viz. MgOHOCH₃ and HOMgOCOOCH₃.

Therefore, the following chain of reactions, considering the case ofmethanol, is deemed beneficial for formation of Mg_(x)CO_(y) materialdisclosed herein:

-   -   Route 1 (monomethyl hydroxycarbonate route):

-   -   Route 2 (hemicarbonic acid route):        CO₂+CH₃OH        CH₃OCOOH        MgO+HOCOOCH₃        MgOCOOCH₃ (as above)    -   Route 3 (orthocarbonate route):

The routes 1, 2, and 3 are non-exclusive and may well occur in parallelunder mild CO₂ pressure (1-12 bar) and T=20-70° C. One skilled in theart will also understand that if the reaction involving theseintermediates is conducted in another solvent than alcohol the suitabletemperature range will depend on the boiling and freezing of the saidsolvent. It is noteworthy that the final product of reactions accordingto routes 1, 2, and 3, viz. HOMgOCOOCH₃, is a labile substance due tothe hydroxyl group present in the vicinity of methoxide group andtherefore could produce a solvate of Mg_(x)CO_(y) with alcohol ofcrystallization, i.e. Mg_(x)CO_(y).CH₃OH. Upon mild heatingMg_(x)CO_(y).CH₃OH readily releases its alcohol of crystallization andproduces a micro- and/or mesoporous powder of Mg_(x)CO_(y) as disclosedherein. Some possible reactions involving alcohol of crystallization areshown below:

-   -   Final:

That the product of Mg_(x)CO_(y).CH₃OH drying, e.g. at 70° C., isMg_(x)CO_(y) was verified using FTIR spectroscopy. Obviously, thematerial can also be heated at higher temperatures as long as it doesnot decompose but this will be related to unnecessary energy consumptionin industrial settings.

Upon visual observation, the degradation goes through several stepssince first a gel like consistency is seen which then turns into a whiterock, identified as amorphous, anhydrous Mg_(x)CO_(y). The moldistribution of the constituent elements, i.e. Mg, C, and O, in thefinal product suggested that the material can contain any of thefollowing species MgCO₃, MgCO₃*MgO, and/or Mg₂CO₄, which at this pointcould not be discerned due to the amorphous nature of the product.

Surprisingly, it was observed that the vapors/gases formed during thedrying of the liquid phase cannot escape readily through the viscous gelphase and therefore act as templates around which the solidificationoccurs. These bubbles form the micro and/or mesopores in the producedMg_(x)CO_(y) material and also stand for the extraordinarily high porevolume and surface area of the material disclosed herein. That the gasesare trapped in the gel was further exemplified when vacuum (200 mbar)was employed to accelerate the drying at 70° C.: the semisolid phasebehaved then as if it was boiling.

Brief synopsis of the mechanism, method, and possible importantintermediates includes the following:

-   -   Routes 1 (monomethyl hydroxycarbonate route), 2 (hemicarbonic        acid route), and 3 (orthocarbonate route) have not been        previously shown to lead to formation of MgOHOCOCH₃;    -   MgOHOCOOCH₃ could be a labile but important intermediate which        could readily produces a solvate of Mg_(x)CO_(y).CH₃OH;    -   MgOHOCH₃ and HOCOOCH₃ could be other important intermediates for        producing MgOHOCOOCH3;    -   Upon mild heating (50-70° C.) of Mg_(x)CO_(y).CH₃OH, produced        from MgOHOCOOCH₃ in methanol, a micro- and/or mesoporous        Mg_(x)CO_(y) is formed;    -   It is currently believed that the evaporating gases, alcohol of        crystallization and CO₂ gas trapped in the solvent, from the gel        phase of Mg_(x)CO_(y).CH₃OH act as templates around which the        solidification of Mg_(x)CO_(y) occurs;    -   The reaction of micro- and/or mesoporous Mg_(x)CO_(y) formation        is facilitated by mildly pressurizing the reaction vessel        whereas the mere bubbling of CO₂ gas through the reaction medium        does not produce the desired product. Under mild pressure        conditions a gel phase is formed which is believed to be        beneficial for the properties of the final product.    -   It is further believed to be beneficial to heat the solution of        MgO in CH₃OH prior to or during pressurizing at 40-70° C.

The method according to the invention forming the amorphous magnesiumcarbonate comprises the formation of a liquid or gel, and theirsubsequent solidification to form a powder or any other solid statemass. Gels may be obtained from the liquids by allowing the liquid toform a gel using any of the following methods, but not limited to,prolonged reaction time, adjustment of the temperature and/or pressure,or changing any other condition obvious for a person skilled in the artthat forces the liquid to turn into a gel. The solid magnesium carbonateof the present invention is further obtained by solidification andsubsequent drying of the gel or liquid at atmospheric, above-atmosphericor below-atmospheric pressure. Non limiting examples ofsolidification/drying processes include tray-drying, vacuum drying,spray-drying, freeze-drying, spray-freeze-drying, supercritical dryingor any other known industrial or otherwise feasible drying process attemperatures below 350° C., i.e. the temperature of magnesium carbonatedecomposition. The solidification and drying of the gel or liquidresults in a coarse solid mass that can be ground or similarlytransformed into a fine powder.

Experimental Synthesis of the Liquids

The amorphous magnesium carbonate according to the present invention areformed starting from opaque or translucent liquids formed in a reactionbetween one or several magnesium containing compounds (chosen from MgO,Mg(OH)₂ and/or any of their respective Mg containing alcoxides chosenfrom alcohols, having a generic formula of R—OH in which R is anyaliphatic or aromatic group, subject to limitations shown in examplesbelow) with pressurized (above atmospheric pressure) carbon dioxide (orany other compound which can serve as the source of it) in an organicsolvent, wherein one of the components is preferably but not necessarilyalcohol. Non-limiting examples of alcohols include methanol, ethanol,n-propanol, isopropanol, butyl alcohol, pentanol, hexanol, heptanol,octanol, ethylene glycol, glycerine, phenol, or benzoyl alcohol.Optionally, water may form in situ during reaction or may optionally beadded to facilitate the reaction in quantities between 0 and 10 vol %.Non limiting examples of additional organic solvent components, whichcan be both water miscible and immiscible, include acetone,acetonitrile, benzole, chloroform, dichlormethane, diethylether,diisopropylether, dimethylformamide, dioxane, methylesther of aceticacid, ethylesther of acetic acid, n-hexane, cyclohexane,dimethylsulfoxide, pyridine, tetrahydrofurane, toluol, or xylol. Non-Mgcontaining compounds may optionally be part of the reaction inquantities not exceeding the weight of the Mg-containing compound. Nonlimiting examples of such materials include CaCO₃, SrCO₃, BaCO₃, ZnCO₃,Al₂(CO₃)₃, SrO, BaO, CaO, ZnO, Zn(OH)₂, Sr(OH)₂, Ba(OH)₂, Ca(OH)₂,Al(OH)₃ and SiO₂ and/or any of their respective alcoxides with alcoholshaving a generic formula of R—OH, wherein R is any aliphatic or aromaticgroup.

In a further embodiment one type of liquid is formed in a reactionbetween MgO and carbon dioxide (at above atmospheric pressure) in areaction medium in which one of the components is an organic solvent,more preferably alcohol.

In one embodiment one type of liquid is formed in a reaction between Mgalcoxide and carbon dioxide at above-atmospheric pressure in which thereaction medium is an organic solvent, which may or not be watermiscible, more preferably alcohol.

In yet another embodiment one type of liquid is formed in a reactionbetween Mg containing compound and carbon dioxide at above-atmosphericpressure in which the reaction medium is methanol.

In yet another embodiment one type of liquid is formed in a reactionbetween Mg containing compound and carbon dioxide at above-atmosphericpressure in which the reaction medium is a mixture between alcohol andanother organic solvent, which may or not be water miscible. No limitingexample of organic solvent includes acetone, acetonitrile, benzole,chloroform, dichlormethane, diethylether, diisopropylether,dimethylformamide, dioxane, methylesther of acetic acid, ethylesther ofacetic acid, n-hexane, cyclohexane, dimethylsulfoxide, pyridine,tetrahydrofurane, toluol, or xylol.

Synthesis of Gels

In one embodiment of the invention, gels are formed from the liquid byallowing the liquid to harden into a gel. This can be obtained viamethods such as, but not limited to, prolonged reaction time, adjustmentof the temperature and/or pressure, or changing any other condition thatforces the liquid to turn into a gel.

Synthesis, Solid Material

One embodiment of the present invention results in a solid materialformed by solidification and subsequent drying of the gel or liquid atatmospheric, above-atmospheric or below-atmospheric pressure. Nonlimiting examples of solidification/drying processes includetray-drying, vacuum drying, spray-drying, freeze-drying,spray-freeze-drying, supercritical drying or any other known industrialor otherwise feasible drying process at temperatures below 350° C., i.e.the temperature of magnesium carbonate decomposition.

One embodiment of the present invention includes one type of powderformed by spray-drying the liquid having set the outlet temperature ofthe spray-dryer above the boiling point of the organic solvent or themixture thereof used to produce the liquid, while the inlet temperatureis set above the outlet temperature of the spray-dryer.

Synthesis, Film and Coating

One embodiment of the present invention includes coherent films orcoatings formed by solidification and subsequent drying of the gel orliquid applied to a surface at atmospheric, above-atmospheric orbelow-atmospheric pressure. Non limiting examples ofsolidification/drying processes include tray-drying, vacuum drying,freeze-drying, spray-freeze-drying, supercritical drying or any otherknown industrial or otherwise feasible drying process at temperaturesbelow 350° C., i.e. the temperature of Magnesium carbonatedecomposition. The solidification and drying of the gel or liquidresults in a coherent and solid film or coating.

Synthesis, Dried Powder

One embodiment of the present invention includes providing dried powderwhich is formed in any of the ways described above and subsequentlyheat-treated at temperatures below 350° C. for 10 minutes or longer.

Mixtures

In one aspect of the invention the amorphous magnesium carbonate isintroduced as part of a composite, composition, mixture, formulation orother system (hereafter referred to as a composite) into which theamorphous magnesium carbonate may be incorporated using various methodsincluded, but not limited to, mixing, spray drying, molding, or otherfeasible method of making a composite. The purpose of introducing theamorphous magnesium carbonate according to the invention in suchcomposite could be any, including, but not limited to improving thefunctionality or introduction new functionality to a composite in e.g.water sorption processes.

Surface Coatings

In one embodiment of the invention, the amorphous magnesium carbonate isused in surface coatings alone or as part of a composite as describedabove. The surface coating can be deposited on any substrate throughsurface deposition techniques such as, but not limited to, spin coatingand electrophoretic deposition. The rationale for using the amorphousmagnesium carbonate in a surface coating could be, but is not limitedto, to improve and/or add functionality to a product

The synthesis of the materials can be divided into three steps asdescribed below:

[Step 1] Mixing a Mg-containing precursor and an alcohol-containingliquid in a reactor, examples of possible ingredients are discussedabove. The mixing is preferably performed under stirring and theconsistency of the mixture is preferably of liquid character. Duringthis step, the ingredients in the mixture react to form one or severalintermediates that later can interact with CO₂. The mixture ispreferably heated in order to facilitate reactions between theingredients in the mixture. The reactor can also be pressurized tofacilitate reaction between the ingredients or control the boilingtemperature of the alcohol-containing liquid. Temperatures between 40°C. and boiling temperature of the liquid are preferable for the reactionto occur, however lower temperatures down to the freezing temperature ofthe liquid is enough for a less complete reaction. This step typicallytakes about 3 h to 24 h at 50° C. for liquid volumes of 100 to 3000 ml.Generally, a slightly yellow (transparent to opaque) liquid product isformed during this step. Higher temperatures reduce the time needed forreaction to take place. The CO₂ pressure during this step can range from0.001 to 200bar above atmospheric pressure, however pressures below10bar are preferable. [Step 2] Reacting the mixture with CO₂. In thisstep, the intermediate products formed during step 1 interact with CO₂to form one or several types of carbonated intermediate products. Thereaction is preferably performed under stirring to facilitate reaction.This step can be performed at temperatures ranging from the freezingtemperature to the boiling temperature of the liquid, and at CO₂pressures ranging from 0.001 to 200 bar above atmospheric pressure.However, temperatures below 50° C. and pressures below 5 bar arebeneficial for carbonation of the intermediate products. During thisstep, the carbonated intermediate products can form a gel in thereactor, typically this occurs after 4-6 days if the CO₂ pressure is 1bar and the temperature is 20° C. during step 2. Increasing the pressureor adjusting the temperature can result in faster gel formation.However, the gel formation is not crucial for formation of the finalmagnesium carbonate in step 3. Generally step 2 takes 1-5 days, longerreaction times result in a higher yield of magnesium carbonate in thefinal material obtained in step 3. [Step 3] Solidification and drying ofthe material. In this step, the liquid or gel formed in the reactorduring step 2 is dried in order to obtain a solid material. During thisstep, the carbonated intermediate products formed during step 2 aretransformed into anhydrous magnesium carbonate. A solidification of thematerial is associated with this drying process and the transformationto magnesium carbonate is facilitated when the products from step 2 aredried at temperatures between 60° C. and 300° C. However, thetransformation to magnesium carbonate also occurs at lower temperaturesbut can take up to several weeks if the drying is performed at roomtemperature. Depending on the intermediates formed during step 1 and 2,presence of water during step 3 could facilitate the transformation tomagnesium carbonate via hydrolysis. After complete transformation of theintermediate products formed in step 2 to magnesium carbonate, traces ofunreacted Mg-containing precursor material can reside in the finalproduct. Careful considerations regarding the conditions during step 1and 2 can minimize the amount of unreacted precursor material in thefinal product. The drying and solidification process in step 3 caninclude techniques such as spray drying or oven drying.

Specific Example

In a preferred embodiment of the invention MgO is used as theMg-precursor and methanol (CH₃OH) as the alcohol and the steps of themethod comprise:

[Step 1] Mixing a Mg-containing precursor and an alcohol-containingliquid: MgO (e.g. 4 g) and methanol (CH₃OH) (e.g. 60 ml) are mixed, thesuspension is heated to between 50° C. and 70° C. for 3-4 hours to formthe intermediate Mg(OH)(OCH₃), most preferably to 50° C. The solution iscontinuously stirred during this step. [Step 2] Reacting the mixturewith CO₂: The solution, now containing Mg(OH)(OCH₃), is pressurized with1-3 bar above atmospheric pressure CO₂ to form the intermediateMg(OCO)(OCH₃)₂ and/or Mg(OCO)(OCH₃)(OH),. The CO₂ pressure can beapplied during step 1 as well, i.e. when MgO and methanol is mixed. Atthis point the temperature is between room temperature (i.e. 25° C.) andup to about 55° C. The solution is continuously stirred during thisstep. Higher temperatures decreases the solubility of CO₂ in the liquid,which is negative for the reaction since CO₂ is needed not only to formthe intermediates described above, but also since extra CO₂ willdissolve in the liquid and physically bond to the same intermediates.CO₂ dissolved in the liquid and CO₂ physically bonded to theMg(OCO)(OCH₃)₂ and/or Mg(OCO)(OCH₃)(OH) is responsible for the formationof the micropores in the material when it is released as gas upondepressurization of the reaction vessel and then causes an expansion ofthe material. Hence, pressure and an excess of CO₂ is needed during thisstep for the later formation of pores in material, i.e. for a completetransformation of MgO to MgCO₃ and also formation of micropores, theCO₂:MgO molar ratio needs to be higher than 1:1. This reaction stepwhere Mg(OCO)(OCH₃)₂ and/or Mg(OCO)(OCH₃)(OH) is formed continues forapproximately 2-4 days. A higher temperature and pressure leads to afaster gel formation but also to a less complete reaction.A) Depressurizing:

-   -   After 3-4 days the reaction vessel is depressurized, the        depressurization is done fast, i.e., within minutes. It is at        this point the micropores in the material are formed when the        dissolved and physically bound CO₂ is released as described        above. To allow the liquid/gel to expand upon release of CO₂,        the pressure of the CO₂ gas is reduced to atmospheric pressure,        i.e. from 1 to 0 bar above atmospheric pressure, in the reactor        and at the same time the temperature is increased to 70-100° C.        in order to decrease the solubility of the CO₂ in the liquid/gel        and to solidify the material. If the material is in the form of        a liquid at this point it turns into a gel in a matter of        minutes when the temperature is raised and the solution is        depressurized. A visible swelling of the gel can be observed at        this time before the material solidifies completely. At this        point, a temperature at or above 70° C. is recommended in order        to solidify the material rapidly since this will conserve the        micropores in the material, a low temperature at this stage will        produce a material with a lesser amount of micropores.        B) Drying:    -   To dry the material a furnace, rotary evaporator or other drying        equipment can be used. During the drying of the material the        mean pore size increases a bit (from approximately 3 nm up to        about 7 nm). When the material is being dried the organic groups        that remains in the material from the synthesis are being        released which is what causes the pore size increase. For a        complete removal of the organic groups (i.e. a “pure” material)        drying above 250° C. is needed, the purity of the material is        increased with the drying temperature.

To analyze the material synthesised in the specific example thefollowing methods and equipment may preferably be used:

Nitrogen sorption measurements can be carried out at 77 K using an ASAP2020 from Micromeritics. The samples are degassed at 95° C. under vacuumfor 10 h prior to analysis with a vacuum set point of 10 μm Hg. Thespecific surface area (SSA) are determined by applying the 5 pointBrunauer-Emmet-Teller (BET) equation (Brunauer S, Emmet P H, Teller E, JAm Chem Soc, 1938, 60:309) to the relative pressure range 0.05-0.30 ofthe adsorption branch of the isotherm. The pore size distribution aredetermined using the DFT method carried out with the DFT Plus softwarefrom Micrometrics using the model for nitrogen adsorption at 77 K forslit-shape geometry with no-negative regularization and high smoothing(λ=0.02000).

X-ray diffraction (XRD) analysis can be performed with a Bruker D8TwinTwin instrument using Cu—K_(α) radiation. Samples are ground and puton a silicon zero background sample holder prior to analysis. Theinstrument are set to operate at 45 kV and 40 mA. Analyses of thediffractogram can be performed using the software EVA V2.0 from Bruker.

Infrared spectroscopy (FTIR) can be performed with a Bruker Tensor27instrument using a Platinum ATR diamond cell. A background scan arerecorded prior to the measurement and subtracted from the samplespectrum, 32 scans are signal-averaged for each spectrum.

The effects of drying at an elevated temperature is shown in FIG. 30where the Evolved gas evolution (EGA) data from a representative sampleof the magnesium carbonate according to the invention is shown. EGAdetects the decomposition products from a material, and in FIG. 30 itcan be seen that between 100-250° C. CO₂ and H₂O is detected. This isdue to remaining —OH and —OCH₃ groups in the material, above 250° C. thecarbonate decomposes which can be seen by the massive formation of CO₂above this temperature. FIG. 31 shows the growth in pore size atdifferent time points for a material stored at 70° C. and also calcinedat 300° C., associated with decomposition of the organic groups. Thepore size distribution for the as-synthesised material (triangle), whichis the material directly after step 3B above that has been dried at 70°C., the same material stored for 1 (circle) and 3 (star) months at 70°C. and the same material that has been calcined (square), i.e. dried at300° C., are shown. Table 1 displays the pore volume and surface areasassociated with the increased pore size due to decomposition of theorganic groups.

TABLE 1 Representative values for specific surface area (SSA), porevolume and mean pore widths for the material after different storageconditions, as measured using nitrogen sorption As- 1 month 3 monthsCalcined Sample synthesized 70° C. air 70° C. air 300° C. N₂ SSA[m²/g]^(a) 638 ± 5  397 ± 3  387 ± 2  265 ± 1  Total pore 0.36 0.50 0.510.42 volume [cm³/g]^(b) DFT Pore 2.5  4.7  5.0  5.5  width [nm]^(c)Limiting 0.21 ± 0.00 0.13 ± 0.00 0.13 ± 0.00 0.10 ± 0.00 microporevolume [cm³/g]^(d) ^(a)Established with the BET equation, using 5 pointsin the relative pressure range from 0.05 to 0.3 ^(b)Single pointadsorption at P/P₀ ≈ 1 ^(c)Established by DFT analysis of the nitrogenadsorption isotherm ^(d)According to the D-A equation, the divergencefor all the values are less than 0.001

The understood reaction mechanisms in the preferred embodiment asdescribed above are:MgO+CH₃OH⇄Mg(OH)(OCH₃)CH₃OH+CO₂⇄

CH₃OCOOHCH₃OCOOH+Mg(OH)(OCH₃)→Mg(OCO)(OCH₃)(OCH₃)+H₂OMg(OCO)(OCH₃)(OCH₃).xCO₂+H₂O⇄Mg(OCO)(OCH₃)(OH).xCO₂+CH₃OHMg(OCO)(OCH₃)(OH).xCO₂→MgCO₃.CH₃OH→MgCO₃+CH₃OH.xCO₂

In another laboratory experiment the amorphous magnesium carbonateaccording to the invention is formed in a reaction between 120 mlmethanol and 8 g MgO in a CO₂ atmosphere, leading to the formation of agel, and subsequent solidification and drying of the obtained product.The initial temperature in the reaction vessel containing methanol andMgO is set to 50° C. and the CO₂ pressure is set to 3 bar (aboveatmospheric pressure). After 4 h, the temperature is lowered to 25° C.and the pressure is lowered to 1 bar (above atmospheric pressure) in thereaction vessel. After a couple of hours of reaction, the initiallymilky white suspension turns into an opaque or translucent yellowishliquid. After about 4 days, a gel formation occurs in the reactionvessel and the reaction is deliberately terminated by a gentledepressurization of the reaction vessel. The gel is subsequentlytransferred onto a tray and dried in an oven set to 70° C. which leadsto a solidification and drying of the gel. In this particular case, thesolidification process takes less than 1 h while the drying processtakes several days. After being dried, the solidified material is groundto a powder, using e.g. ball milling. It is obvious that one skilled inthe art can choose from several available grinding processes such asmortar, impact, attrition, jet grinding or any other industriallysuitable type. Alternatively the powder is heat-treated after thesolidification and drying as described above prior to the grinding.After drying above 250° C. the powder obtained a surface area of 240m²/g and a total pore volume of 0.42 cm³/g.

In further experiments the amorphous magnesium carbonate according tothe invention is formed in a reaction between 120 ml methanol and 8 gMgO in a CO₂ atmosphere, leading to formation of a liquid and subsequentsolidification and drying of the obtained product. The initialtemperature in the reaction vessel methanol and MgO is set to 50° C. andthe CO₂ pressure is set to 3 bar (above atmospheric pressure). After 4h, the temperature is lowered to 25° C. and the pressure is lowered to 1bar (above atmospheric pressure) in the reaction vessel.

After a couple of hours of reaction, the initially milky whitesuspension turns into a slightly yellow liquid. After 2 days, thereaction is deliberately terminated by a gentle depressurization of thereaction vessel. The liquid is subsequently transferred to a tray anddried in an oven set to 70° C. which leads to a solidification anddrying of the liquid. In this particular case, the solidificationprocess takes less than 1 h while the drying process takes several days.After being dried, the solidified material is ground to a powder, usinge.g. ball milling. It is obvious that one skilled in the art can choosefrom several available grinding processing such as mortar, impact,attrition, jet grinding or any other industrially suitable type.Alternatively the powder is heat-treated after the solidification anddrying as described above prior to the grinding.

Currently preferred materials to start the reaction of forming theamorphous magnesium carbonate include MgO, CO₂ and an alcohol, such ase.g. methanol.

Two aspects of the method of synthesizing the amorphous magnesiumcarbonate according to the invention deserve further discussion. If CO₂is merely passed (bubbled) through a methanolic suspension of MgO oranother magnesium containing material at atmospheric pressure, noreaction is observed. During the development of the particular amorphousmagnesium carbonate materials, we surprisingly found that moderatelypressurized CO₂ gas (preferentially ˜1-3 bar above atmospheric pressureor higher) in a sealed container saturated with CO₂ converts MgO toanhydrous magnesium carbonate in methanol. Nothing in the previous arthas suggested that (a) anhydrous magnesium carbonate can be produced inalcoholic suspensions and (b) that moderate pressure will be mostfavorable to produce the desired effect. On the contrary, earlierteachings suggested that Magnesium carbonate cannot be obtained frommethanolic suspensions, unlike the carbonates of Ca, Ba and Sr. We havealso further observed that CO₂ pressure in the reaction vessel has adrastic impact on the gelation time, which is decreased threefold whenthe pressure is kept at 3 bar over atmospheric pressure throughout thereaction. We have also observed that the excessive pressure may alsoresult in a lower yield of magnesium carbonate in the final product andproduce more traces of unreacted MgO.

EXAMPLES Example 1

MgO 8 g Methanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

8 g MgO powder was placed in a glass bottle together with 120 mlmethanol and a stirring magnet. The solution was put under 3 bar aboveatmospheric pressure CO₂ pressure and heated to 50° C. Afterapproximately 3 hours the mixture was allowed to cool to roomtemperature and the CO₂ pressure was lowered to 1 bar above atmosphericpressure. The initially milky white suspension in the reaction vesseltransformed gradually into a slightly yellowish liquid in the reactionvessel after a couple of hours. The reaction continued for about 4 daysuntil a gel had formed in the reaction vessel. Subsequently the pressurein the reaction vessel was brought to atmospheric pressure and the gelwas collected and put onto a tray for drying in an oven at 70° C. Thelatter caused the gel to solidify within an hour. The solidifiedmaterial was left in the oven to dry for 2 days.

Material Characterization Example 1

The dried material formed a coarse powder that was primarily amorphouswith traces of unreacted and crystalline MgO, see X-Ray Diffraction(XRD) pattern in FIG. 1. The sharp peaks at 43° and 62° 2θ originatefrom the unreacted MgO while the halo peak between 25° and 40° 2θ isindicative of at least one amorphous phase.

Raman spectroscopy reveals that the powder is indeed composed ofmagnesium carbonate, see FIG. 2, where the band at ˜1100 cm⁻¹corresponds to vibration of the carbonate group. Moreover, a broad halo,or the so-called Boson peak, with a maximum at ˜100 cm⁻¹ furtherwitnesses of the amorphous character of the powder.

When examined with Fourier transform infrared spectroscopy (FTIR), seeFIG. 10, the material shows absorption bands at ˜1440 cm⁻¹, ˜1100 cm⁻¹and ˜850 cm⁻¹ which all correspond to the carbonate group. No water ofcrystallization is visible in this spectrum.

The anhydrous character of the bulk material is further confirmed byThermal Gravimetric Analysis (TGA), see FIG. 3, where the loss with amaximum at 150° C. is due to loss of remaining organic groups. X-rayphotoelectron spectroscopy (XPS) confirms the anhydrous nature of themagnesium carbonate: Energy resolved spectra were recorded for theMg_(2p) and O_(1s) peaks, see FIGS. 9 and 11. The position of theMg_(2p) peak at 52.1 eV and O_(1s) peak at 533.5 eV are indicative ofmagnesium carbonate, and the O_(1s) peak does not contain any componentsfor crystal water, which otherwise would have appeared at 533-533.5 eV.The shoulder seen at 535.6 eV is located between the binding energiesfor liquid water (539 eV) and ice (533 eV) and hence is representativefor surface adsorbed water as previously described for surface adsorbedwater on carbon fibers. The shoulder seen at 531.0 eV shows the presenceof MgO in the powder. No presence of Mg(OH)₂ was observed in the bulkwhich, expectedly, would have resulted in a peak at 532.4 eV.

In order to analyze the pore structure and water sorption capacity ofthe produced amorphous magnesium carbonate according to the presentinvention, N₂ and H₂O vapor sorption analyses were carried out. FIG. 6shows the N₂ sorption isotherm for the magnesium carbonate according tothe present invention and displays a typical Type 1 shape of theisotherm according to the IUPAC classification, which is indicative of amicroporous adsorbent. The lack of hysteresis between the adsorption anddesorption branches in the N₂ isotherm is a distinct feature formicroporous. FIG. 5 shows the isotherm for H₂O vapor adsorbed on themagnesium carbonate according to the present invention, which providesinformation about the materials interaction with water molecules.

Based on the massive H₂O vapor adsorption at low RHs, it is evident thatthe produced amorphous magnesium carbonate material, according to thepresent invention, strongly interacts with water molecules and shows astrong hydrophilic behavior. The limited amount of desorption from thematerial when the RH is reduced from ˜95% to ˜5% is further proof of thestrong interaction between water molecules and the amorphous magnesiumcarbonate according to the present invention. It should, however, benoted that no signs of hydrate formation of the material is seen usingXRD after the isotherm is completed and that the isotherm can berepeated with similar result after heat treatment of the magnesiumcarbonate according to the present invention at moderate temperature(95° C.).

Both isotherms were analyzed further to establish both the specificsurface area (SSA) of the material according to theBrunauer-Emmet-Teller (BET) equation, and the micro-porous propertiesaccording to the Dubinin-Astakhov (D-A) model, see Table 2.

It should be noted that the total pore volume given in Table 2 refers tothe total volume of pores filled with nitrogen gas at saturationpressure in a nitrogen sorption experiment carried out at 77 K. This isalso the pore volume referred to elsewhere in the text when a porevolume is given without reference to a specific pore size interval.

The hydrophilic nature of the material was further reflected in thegreater characteristic energy for adsorption of H₂O compared to N₂. Thediscrepancy in limiting micro-pore volume (w₀)—in which the valueobtained from the N₂ isotherm is that normally reported in theliterature—and modal equivalent pore size obtained from the twoisotherms is most likely due to site-specific interaction between theH₂O species and the material, not only in the micropores but also on theexterior of the material and in pores larger than 2 nm.

The SSA of the amorphous magnesium carbonate powder according to thepresent invention is observed to be ˜800 m²/g which is up to two ordersof magnitude larger than corresponding values reported for any otherform of magnesium carbonate, with commercial (crystalline) analoguestypically having SSAs of about 4-18 m² g⁻¹. For previously reportedamorphous magnesium carbonate produced by thermal decomposition ofhydrated magnesium carbonate forms, the highest SSA found in theliterature is ˜50 m² g⁻¹. In fact, the SSA observed for the amorphousmagnesium carbonate according to the present inventions isextraordinarily high, not only for magnesium carbonate, but also foralkaline earth carbonates and minerals in general. This places theamorphous magnesium carbonate according to the present invention in theexclusive class of high surface area nanomaterials including meso-poroussilica, zeolites, metal organic frameworks (MOFs), and carbon nanotubes.

TABLE 2 Structural and chemical characteristics of the amorphousmagnesium carbonate according to the present invention obtained from N₂and H₂O vapor isotherms. Adsorbate N₂ H₂O SSA¹ (m²/g) 800 ± 3.60   —Total pore volume (cm³/g) 0.47 — w₀, limiting micropore 0.28 ± 0.0005590.16 ± 0.0102 volume³ (cm³/g) Equivalent surface area in 549 478micropores³ (m²/g) Characteristic energy of 11.4 41.0 adsorption³(kJ/mol) Modal equivalent pore width³ (nm) 1.75 1.09 Correlationcoefficient of fit³ 0.999 0.977 ¹According to the 5-point BET equationapplied in the relative pressure range from 0.05 to 0.3 ² Single pointadsorption at P/P0 ≈ 1 ³According to the Dubinin-Astakhov equation

The pore size distribution (see FIG. 8) of the sample was evaluatedusing the DFT Plus software from Micromeritcs using the model fornitrogen at 77 K on carbon with slit-shaped pores. The DFT-basedcumulative pore size distribution gives that about 98% of the porevolume is constituted by pores with a diameter smaller than 6 nm whilethe remaining pore volume is made up of pores with a broad sizedistribution between 8 and 80 nm centered around 16 nm. As can be seenin FIG. 8 the cumulative pore volume of pores with a diameter smallerthan 10 nm is above 0.40 cm³/g. When examined with scanning electronmicroscopy (SEM), these larger pores are clearly visible in some partsof the material as illustrated in FIG. 12. These larger pores are,however, not visible throughout the entire material, which is consistentwith the limited contribution to the total pore volume from such pores.

The water sorption capacity of the material is interesting from anindustrial and technological point of view and it is, hence, compared tothree commercially available desiccants, viz. fumed silica (SSA: 196 m²g⁻¹), hydromagnesite (SSA: 38 m² g⁻¹) and the micro-porous Zeolite Y(SSA: 600 m² g⁻¹, silica/alumina ratio 5.2:1), see FIG. 5. The H₂O vaporadsorption isotherm for the amorphous magnesium carbonate according tothe present invention displays similarities with the hydrophilic zeoliteat very low RHs (<1%) and shows on an even higher adsorption capacityfor the amorphous magnesium carbonate according to the present inventioncompared to the zeolite at RHs between 1 and 60%. This behaviourcontrasts largely to that of the other two non-porous materials thatmainly adsorb H₂O at RH>60%. The H₂O vapor adsorption behavior for theamorphous magnesium carbonate according to the present invention wasalso studied by dynamic vapor sorption (DVS) which confirmed that thematerial has an extraordinary capacity to adsorb H₂O vapor, even atextremely low RH, a property highly desirable for desiccants in variousapplications. Heating the sample to 95° C. appeared to regenerate thewater sorption capacity without any crystal phase changes.

The characterization described above was utilized, at least partly, forthe examples described below.

Example 2

As described in Example 1 but where the obtained powder was heat-treatedat 70° C. for 7 days. The particles proved to be composed of a materialsimilar to the one in Example 1, viz. amorphous and anhydrous magnesiumcarbonate with traces of MgO. However, the specific surface area provedto be 454 m²/g, with a distinct pore size distribution around 6 nm. Ascan be seen in FIG. 14 the cumulative pore volume of pores with adiameter smaller than 10 nm is above 0.7 cm³/g. The nitrogen sorptionisotherm and the pore size distribution obtained via DFT analysis of thenitrogen isotherm for this sample is displayed in FIGS. 13 and 14,respectively. This well-defined pore size distribution is similar tothose found in ordered mesoporous silica materials and seldom foundelsewhere. Also this material was associated with a H₂O vapor sorptionisotherm similar to the one described in Example 1.

Example 3

As described in Example 1 but where the liquid was spray-dried before agel was formed in the reaction vessel.

The liquid obtained after the reaction between MgO and methanoltransformed into particles when spray-dried. The particles proved to becomposed of a material similar to the one in Example 1, viz. amorphousmagnesium carbonate with traces of MgO. The average particle size wasapproximately 1 nm in diameter as determined by SEM analysis, SEM imagein FIG. 15. The surface area of the obtained particles was 68.5 m²/g asdetermined by BET analysis.

The water vapor sorption of the spray-dried material at different RHranging from 0-100% is displayed in FIG. 16. As can be seen in FIG. 17the cumulative pore volume of pores with a diameter smaller than 10 nmis above 0.018 cm³/g. The nitrogen sorption isotherm for the magnesiumcarbonate of the present invention in this example is displayed in FIG.18.

When 0.8 g dried magnesium carbonate of the present invention producedin this example was put in a sealed chamber with 100% RH at roomtemperature, the weight of the sample increased to 2.2 g by adsorptionand uptake of water within 48 h as displayed in FIG. 20. The materialcontinued to gain weight for several days.

Example 4

As described in Example 1 but with the material prepared with ethanolinstead of methanol

MgO 8 g Ethanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

The attempt with ethanol as solvent did not result in any visible gelformation in the reaction vessel. However, when the liquid was placed inan oven set to <70° C., it formed a gel that solidified and latertransformed into a powder when dried. This powder contained largeamounts of unreacted MgO, but it also shared some the characteristics ofthe previously prepared powders in Example 1. It also containedmagnesium carbonate, which is suggested to be the reason for thesolidification of the ethanolic liquid once placed in the oven asverified with XRD. Surprisingly, the surface area of this material was737 m²/g, which is in agreement to the magnesium carbonate produced withmethanol.

After several weeks in the reaction vessel (at room temperature andatmospheric pressure) a clear gel formed at the top of the vessel. Theclear gel also consisted of amorphous magnesium carbonate without tracesof MgO as characterized by XRD and FT-IR. The surface area of thismaterial is 225 m²/g and a pore volume of 1.55 cm³/g. The pore volumefor pores less than 10 nm in width is 0.8 cm³/g, see FIG. 19.

Example 5

As described in Example 1 but prepared with addition of toluene.

MgO 8 g Methanol 46 ml Toluene 74 ml CO₂ (gas) 3 & 1 bar (aboveatmospheric pressure)

The toluene accelerated the formation of magnesium carbonate in thepresent example where the gelation time was reduced compared to whenonly methanol was used, however the surface area of the obtainedmaterial was in this case 222 m²/g and the pore volume was 0.78 cm³/gwith a broader pore size distribution ranging from approximately 4 nmdiameter to 30 nm, with a maximum at 10 nm. The volume of pores width adiameter less than 10 nm is 0.36 cm³/g, see FIG. 21.

Example 6

As described in Example 1 but with a higher amount of methanol, and gelformation through increased temperature. After 4 days of reaction, thetemperature in the reaction vessel was increased to 30° C. which causedthe liquid to turn into a gel.

MgO 8 g Methanol 140 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

The obtained amorphous magnesium carbonate according to the presentinvention proved to be composed of anhydrous and amorphous magnesiumcarbonate and crystalline MgO as in Example 1. The magnesium carbonateaccording to the present invention in this example had a surface area of400 m²/g, a pore volume of 0.97 cm³/g and a narrow pore sizedistribution around 8 nm. The volume of pores with a pore diameter lessthan 10 nm is 0.91 cm³/g, see FIG. 22.

Example 7

As described in Example 1 but with a higher synthesis pressure.

MgO 8 g Methanol 120 ml CO₂ (gas) 3 bar (above atmospheric pressure)

In this experiment, the gas pressure was kept a 3 bar until a gel hadformed in the reaction vessel. This led to a faster reaction (3 timesfaster) as compared to Example 1. The obtained material proved once moreto consist of amorphous and anhydrous magnesium carbonate with traces ofMgO as described in Example 1. The surface area measured via gasadsorption for the material obtained in this experiment was 309 m²/gwith a pore volume of 0.575 cm³/g. The DFT-based pore size distributionshowed pore diameters between 4-8 nm, with a maximum around 6 nm. Thevolume of pores with diameter less than 10 nm is 0.53 cm³/g, see FIG.23.

Example 8

As described in Example 1 but with a lower amount of MgO, and gelformation through increased temperature. After 4 days of reaction, thetemperature in the reaction vessel was increased to 40° C. which causedthe liquid to turn into a gel.

MgO 6 g Methanol 120 ml CO₂ (gas) 1 bar & 3 bar (above atmosphericpressure)

The obtained magnesium carbonate according to the present inventionproved to be composed of anhydrous and amorphous magnesium carbonate andcrystalline MgO as in Example 1. The surface area of the obtainedmaterial was 284 m²/g with a total pore volume of 0.93 cm³/g and anarrow pore size distribution around 8.5 nm. The volume of pores withdiameter less than 10 nm is 0.54 cm³/g, see FIG. 24.

Example 9

As described in Example 1 but with a lower synthesis temperature.

MgO 8 g Methanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

In this experiment, the reaction temperature was kept at roomtemperature until a gel had formed in the reaction vessel. This led to asignificantly slower reaction as compared to Example 1. The obtainedmaterial proved once more to consist of amorphous and anhydrousmagnesium carbonate with traces of MgO as described in Example 1 withsimilar characteristics.

Example 10

As described in Example 1 but with addition of various amounts ofCa(OH)₂.

MgO/Ca(OH)₂ ratio 1:1-1:0 (8 g) Methanol 120 ml CO₂ (gas) 3 & 1 bar(above atmospheric pressure)

Increasing amounts of Ca(OH)₂ in the powder phase prior to the reactionled to increasing amounts of amorphous CaCO₃ in the resultant material.Storing the materials at high relative humidities for an extended timecrystallized the amorphous CaCO₃ content in the amorphous magnesiumcarbonate according to the present inventions. Amorphous and anhydrousmagnesium carbonate was still obtained throughout the experiments.

When prepared with 5 wt % Ca(OH)₂ in the powder phase, the surface areaof the material of the present invention was 570 m²/g, with a total porevolume 0.63 cm³/g and a narrow pore size distribution around 4.5 nm. Thevolume of pores with diameter less than 10 nm is 0.58 cm³/g, see FIG.25.

Example 11

As described in Example 1 but with addition of various amounts of SrO.

MgO/SrO ratio 1:1-1:0 (8 g) Methanol 120 ml CO₂ (gas) 3 & 1 bar (aboveatmospheric pressure)

Increasing amounts of SrO in the powder phase prior to the reaction ledto increasing amounts of crystalline SrCO₃ in the resultant material.Amorphous and anhydrous magnesium carbonate was still obtainedthroughout the experiments.

Example 12

As described in Example 1 but with addition of various amounts of BaO.

MgO/BaO ratio 1:1-1:0 (8 g) Methanol 120 ml CO₂ (gas) 3 & 1 bar (aboveatmospheric pressure)

Increasing amounts of BaO in the powder phase prior to the reaction ledto increasing amounts of crystalline BaCO₃ in the resultant material.Amorphous and anhydrous magnesium carbonate was still obtainedthroughout the experiments.

Example 13

As in example 3 but spin coated instead of spray dried.

The liquid was spin coated onto a silicon wafer and dried at 70° C.,which resulted in a coating of amorphous magnesium carbonate accordingto the present invention on the silicon wafer.

Example 14

As in Example 3 but where the liquid was filtered through a filtermembrane having a pore size cut-off of at about 200 nm to obtain aclear, transparent liquid. The liquid was then stored at 1 bar (aboveatmospheric pressure) with CO₂ gas until a gel was formed. The gel wasthen transferred onto a tray and placed in an oven at 70° C. to solidifyand dry. The obtained product consisted of high purity anhydrous andamorphous magnesium carbonate of the present invention.

Example 15

As described in Example 1 but where reaction vessel was depressurizedbefore a gel had formed (after 3 days of reaction) and where the liquidwas left in the vessel at room temperature and ambient conditions for 2weeks before placed in an oven at 70° C.

MgO 8 g Methanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

The liquid formed in the reaction vessel transformed into a gel when itwas left standing for 24 at ambient conditions. When the gel was placedin the oven after 2 weeks it solidified and the material was dried out.This produced a solid material with the same composition as described inExample 1, i.e. amorphous and anhydrous magnesium carbonate with tracesof MgO. However, the SSA of the final material in this example wassubstantially lower (77 m2/g) as compared to the material in Example 1and had a total pore volume of 0.47 cm³/g with a distinct pore sizedistribution around 20 nm, see FIGS. 26 and 27. The pore volumecorresponding to pores smaller than 10 nm in diameter was only 0.0043cm³/g in this example, as illustrated in FIG. 27, which essentiallycorresponds to an absence of micro pores according to the definitionused herein. The absence of micro pores and the low pore volume in thefinal material produced in this example caused a drastic decrease inwater vapor sorption capacity as compared with the materials in Examples1 and 2. The water sorption characteristics of the material in thisexample is displayed in FIG. 28.

Example 16

As described in Example 1 but with various temperatures and pressuresduring the initial stage of the synthesis reaction. The initial stage ofthe reaction is the time it takes for the slightly yellow liquid to form(approx. 3 hours in Example 1).

MgO 8 g Methanol 120 ml Initial reaction CO₂ pressure 0.001 bar to 79bar (above atmospheric pressure) Initial reaction temperature From 0° C.to just below boiling temperature (max 100° C.) Later reaction CO₂pressure 1 bar (above atmospheric pressure) Later reaction temperature25° C.

The boiling temperature of methanol varies with pressure and hence thesynthesis temperature in this example was adjusted so that the methanolnever did boil at the current pressure. Increasing temperatures andpressures in the initial reaction stage resulted in faster formation ofthe slightly yellow liquid in the reaction vessel. At the lowertemperatures and pressures, a change in color was not observed visuallyand the initial stage of the reaction was terminated after 6 hours. Alower yield of magnesium carbonate was obtained in the final materialsfor the synthesis performed at low initial temperature and pressure.

Example 17

As described in Example 1 but with various temperatures and pressuresduring the later stage of the synthesis reaction. The later reactionstage is the phase of the reaction that follows when preferably theslightly yellow liquid has formed.

MgO 8 g Methanol 120 ml Initial reaction CO₂ pressure 3bar (aboveatmospheric pressure) Initial reaction temperature 50° C. Later reactionCO₂ pressure 0.001 bar to 79 bar (above atmospheric pressure) Laterreaction temperature From 0° C. to below boiling (max 100° C.)

The boiling temperature of methanol varies with pressure and hence thesynthesis temperature in this example was adjusted so that the methanolnever did boil at the pressure used. The highest yield of magnesiumcarbonate in the final materials was obtained at pressures around 1 bar(above atmospheric pressure) and temperatures below 50° C. However,various amounts of magnesium carbonate were obtained throughout theexperiments.

Example 18

As described in Example 1 but with higher temperatures during thesolidification step.

Methanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)Solidification temperature 75° C. to 300° C.

This produced magnesium carbonate materials with similar characteristicsas in Example 1.

Example 19

As described in Example 1 but with lower temperatures during thesolidification step.

Methanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)Solidification temperature 25° C. and below

This produced amorphous and low surface area materials.

Example 20

As described in Example 1 but below freezing temperature of methanol.

MgO 8 g Methanol 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

In this case no reaction occurred.

Example 21

As in Example 1 but prepared with pentane instead of methanol

MgO 8 g Pentane 120 ml CO₂ (gas) 3 & 1 bar (above atmospheric pressure)

In this case no reaction occurred.

Example 22

As described in Example 1 but with addition of various amounts of water

MgO 8 g Methanol 120 ml H₂O 5-100 ml CO₂ (gas) 3 & 1 bar (aboveatmospheric pressure)

In this case, crystalline phases of magnesium carbonates were formed. Athigher water concentrations the resultant materials were hydrated whilethe materials formed at lower water concentrations were of moreanhydrous nature.

Example 23

As described in Example 1 but where the CO₂ was bubbled through themethanolic suspension of MgO.

MgO 8 g Methanol 120 ml

In this case no reaction occurred.

Example 24

As described in Example 1 but with 50 volumetric percent of water.

MgO 8 g Methanol 60 ml H₂O 60 ml CO₂ (gas) 3 & 1 bar (above atmosphericpressure)

In this case, crystalline nesquehonite was formed, see FIG. 29. Thematerial had a low surface area and was non-porous and hence thepresence of 60 ml water in 60 ml methanol does not lead to the desiredresult.

Example 25

As described in Example 1 but with Mg(OH)₂ instead of MgO as thestarting material.

Mg(OH)₂ 8 g Methanol 120 ml CO₂ (gas) 1 & 3 bar (above atmosphericpressure)

In this case no reaction occurred, hence the use of Mg(OH)₂ as astarting material when using the same reaction conditions as in example1 does not lead to the desired result.

Example 26

As described in Example 1 but with Mg(OCH)₃ instead of MgO as thestarting material.

Mg(OCH)₃ 50 ml (10 wt % Mg(OCH₃)₂ in methanol) CO₂ (gas) 1 & 3 bar(above atmospheric pressure) Water 0.87 ml

In this example the magnesium methoxide and water were placed in areaction vessel under carbon dioxide pressure, the carbon dioxidepressure was set to 3 bar above atmospheric pressure for the first 3hours and then lowered to 1 bar above atmospheric pressure for theremaining reaction time. The temperature was set to 50° C. for the first3 hours and then room temperature for the remaining reaction time. Thesolution in the reaction vessel turned yellow within 1 hour and after 12hours a powder had formed in the reaction vessel, this powder wascharacterized as magnesium methyl carbonate based on the IR spectra inFIG. 32. Hence in this example no magnesium carbonate was formed andtherefore using these conditions Mg(OCH₃)₂ is not a preferred startingmaterial.

Example 27

The magnesium carbonate material was prepared as in the specific exampleusing a drying/calcination temperature of 250° C. In this example themagnesium carbonate material and the zeolite Y material were dried at250° C. over night, after this both the samples were placed in adesiccator saturated with water vapor, i.e. 100% relative humidity, atroom temperature for 18 hours. After this the regeneration energy werecompared between the two samples using a TGA instrument, more preciselya Thermogravimetric analyzer from Mettler Toledo, model TGA/SDTA851einstrument with a 3° C./min ramping temperature was used. Themeasurements were performed under a flow of air. The result is shown inFIG. 33, as can be seen in the figure at 150° C. the magnesium carbonatematerial according to the present invention has lost 40 wt % more waterthan the Zeolite Y and approximately 65° C. higher temperature is neededfor a complete removal of water in the zeolite Y material as compared tothe magnesium carbonate material.

Example 28

In this example the magnesium carbonate according to the currentinvention is used as a pharmaceutical excipient. As an illustrativeexample amorphous Ibuprofen was formulated using the magnesium carbonateaccording to the present invention.

Introduction to Example 28

During the last decades, poor aqueous solubility of activepharmaceutical ingredients (APIs) has been one of the most challengingissues for the pharmaceutical industry. About 40% of newly marketeddrugs have low solubility and 80-90% of drug candidates in the R&Dpipeline fail due to solubility problems. Due to the poor aqueoussolubility these drugs have low bioavailability and/or a slow onset ofaction, and this may lead to a limited and insufficient therapeuticeffect. Therefore, much effort has been put into solving this issueusing different types of strategies including salt formulations, APIparticle size reduction, use of solubilizers, solid dispersions,co-ground mixtures and pro-drugs. However, there are still practicallimitations of these techniques. For example, the salt formation isavailable for acid and basic drugs, however it is not feasible forneutral compounds and it may be difficult to form salts of very weakbases and acids. Even if a stable salt can be formed, conversion from asalt to a poorly soluble free acid or base can occur both in vitro andin vivo; as to the particle size reduction, this method may lead tobuild-up of static charges and lead to handling difficulties. In thisrespect, preparation and stabilization of the API in its amorphous statehave been suggested. Typically, organic polymers like polyethyleneglycol (PEG) and polyvinyl pyrroline (PVP) are used in solid dispersionsfor this purpose. However, this approach suffers from the problems withchemical stability of products and difficulties in the industrialmanufacturing processes. Recent developments in nanotechnology sciencehave provided new inorganic materials that can be used to stabilizeamorphous APIs. It has been found that mesoporous structures (pores witha diameter between 2 and 50 nm) in materials have the ability toeffectively suppress crystallisation of amorphous substances.

Materials Synthesis for Example 28

Magnesium Oxide (MgO) and ibuprofen were obtained from Sigma-Aldrich,Sweden. Methanol and ethanol were purchased from VWR International,Sweden. CO₂ was obtained from Air Liquide, Sweden. All chemicals wereused as received.

The magnesium carbonate was synthesised as follows: 170 g of MgO and 2.5L CH₃OH was mixed at 500 rpm in a 5 L Ecoclave pressure reactor fromBüchi. The reactor was pressurised with 3 bar CO₂ and the reaction wascarried out at 55° C. After 4 days the temperature was lowered to roomtemperature and the reactor depressurised. The product was dried at 75°C. in a vacuum oven for 3 days and then calcined at 250° C. for 6 hours.Calcination was performed in order to assure decomposition of theorganic intermediates formed in the reaction carried out in the pressurereactor. Upon this decomposition, magnesium carbonate is formed.

Drug Loading Procedure for Example 28

Ibuprofen was incorporated into the magnesium carbonate via a soakingmethod; 203.2 mg ibuprofen was dissolved in 50 ml ethanol and then 642.7mg of the magnesium carbonate was added to the solution. The mixture wasplaced on an orbital shaker at 100 rpm at room temperature for 24 h toallow for diffusion of ibuprofen into the magnesium carbonate.Subsequently the suspension was dried in an oven at 70° C. to evaporatethe solvent leaving a dry product containing 24 wt % of Ibuprofen.

Characterization for Example 28

X-ray powder diffraction (XRD) analysis was performed with a D5000diffractometer (40 kV, 40 mA, Siemens/Bruker) using Cu—K_(α) radiation(λ=0.154 nm). Samples were ground in a mortar and put on silicon sampleholders with zero background prior to analysis.

Fourier transform infrared spectroscopy (FTIR) studies were performed,using a Bruker FTS 66v/s spectrometer with an Attenuated TotalReflectance (ATR) sample holder. All FTIR spectra were collected at aspectrum resolution of 4 cm⁻¹, with 50 scans over the range from 4,000to 500 cm⁻¹. A background scan was acquired before scanning the samples.

N₂ sorption analysis: Gas sorption isotherms were obtained using an ASAP2020 from Micromeritics, operated at 77 K. Prior to analysis the sampleswere degassed under vacuum at 338 K for 12 h prior to measurement. Thespecific surface area (SSA) was calculated using the multipointBrunauer-Emmett-Teller (BET) method while the pore size distribution wascalculated based on density functional theory (DFT) method using themodel for N₂ at 77 K. These calculations were all performed using theASAP 2020 (Micromeritics) software.

Thermal gravimetric analysis (TGA) was carried out on a Mettler Toledo,model TGA/SDTA851e, under an air flow in an inert alumina cup. Thesamples were heated from room temperature to 600° C. with a heating rateof 3 K min⁻¹.

Differential scanning calorimetry (DSC) was performed on a DSC Q2000instrument from TA instruments using Exstar software. Samples of 3.5-5.5mg were weighted into 5 mm Al pans and sealed. Samples were first cooleddown to ˜35° C. and then heated to 150° C. at a heating rate of 3Kmin⁻¹. The instrument was calibrated for melting point and hear offusion (Tm[° C.] and ΔHm[mJ mg⁻¹]) of Indium (156.6° C., 28.4 mJ mg⁻¹).

Drug Release Measurement: The release of ibuprofen was carried out in aUSP-2 dissolution bath (Sotax AT7 Smart, Sotax AG, Switzerland) equippedwith 1000 mL vessels (37° C., 50 rpm). Samples with a total drug contentof 17.5 mg ibuprofen were placed in vessels containing 500 mL phosphatebuffer (pH=6.8). Measurements were made in triplicates on pure ibuprofen(IBU) crystals and ibuprofen loaded magnesium carbonate (MGCO3-IBU).Aliquots of 3 mL were withdrawn from each vessel at regular intervalsfor 125 min and the drug concentration in the liquid samples wasanalysed using UV/vis absorbance spectroscopy (1650PC, ShimadzuCorporation, Kyoto, Japan).

Long-term Stability Test: An MGCO3-IBU sample was stored in a desiccatorat room temperature and 75% RH (obtained with a saturated aqueousmixture of water and NaCl) for 3 months. The sample was then analysedwith XRD and DSC in order to investigate if a humid atmosphere inducescrystallisation of the incorporated ibuprofen. Magnesium carbonatewithout ibuprofen was also stored under the same conditions to examineif the humidity affects the carrier material.

Results for Example 28

After calcination, the Magnesium carbonate was in the form of whitemillimeter-sized particles. The peaks in the obtained XRD patterncorrespond to unreacted MgO in the product while the lack of other peaksrevealed that the magnesium carbonate component in the material isamorphous. The magnesium carbonate component of the material was evidentfrom the FTIR spectra of the material, where absorption bands at ˜850cm⁻¹, ˜1100 cm⁻¹ and ˜1400 cm⁻¹ stem from the carbonate group. The porevolume and mean pore size of the magnesium carbonate, as obtained fromanalysis of nitrogen sorption isotherms, are given in table 3 below.

TABLE 3 Results of material characterizations before and after ibuprofenloading as obtained from N₂ sorption experiments. The BET surface areawas obtained as in above examples. Sample S_(BET) (m²/g) V_(pore)(cm³/g)D_(BJH)(nm) Magnesium carbonate 349 0.833 6.9 MGCO3-IBU 245 0.394 4.9

The pore size distribution obtained from the N₂ sorption analysis isgiven in FIG. 34

After loading the magnesium carbonate with ibuprofen, TGA was carriedout to investigate the drug loading degree in the carrier. From these itwas evident that the free ibuprofen decomposed at about 200° C. whilethe magnesium carbonate in the calcined material before drug loadingdecomposed into MgO and CO₂ at about 370° C. For the MGCO3-IBU sampletwo distinct weight loss regions were observed, the first related to thedecomposition of ibuprofen and the other related to the decomposition ofthe magnesium carbonate. The decomposition temperature of theincorporated ibuprofen was shifted 140° C. to about 340° C. compared tothe free substance. The onset of decomposition for the magnesiumcarbonate was also shifted towards higher temperatures in the MGCO3-IBUsample, from about 320° C. to 350° C. compared to the calcined andunloaded material. From the TGA data it can be calculated that the drugloading degree of ibuprofen in MGCO3-IBU is 24 wt % which corresponds tothe magnesium carbonate/ibuprofen weight ratio in the preparation of thesample.

FTIR for MGCO3-IBU further confirmed successful incorporation ofibuprofen in the magnesium carbonate. In the absorbance spectra for theMGCO3-IBU, no new absorbance bands compared to the free ibuprofen andthe empty magnesium carbonate could be observed. This indicated that theadsorption of the ibuprofen in the pores of the magnesium carbonate wasof physical character.

From the N₂ sorption data it can be seen that the mean pore diameter inthe MGCO3-IBU sample is reduced with 2 nm compared to the emptymagnesium carbonate and that the pore volume is reduced by about 50%.The shift toward smaller pores related to narrowing of the pores in theempty magnesium carbonate when the material is filled with ibuprofen isalso seen in the pore size distribution in FIG. 34.

The XRD pattern for MGCO3-IBU lacks peaks corresponding to crystallineibuprofen indicating a lack of crystallinity of the incorporated drug.The only peaks visible in the MGCO3-IBU XRD pattern stem from the MgO inthe material. The lack of crystallinity of the ibuprofen in theMGCO3-IBU sample was further evident from the DSC curves. Theendothermic event observed in these curves at 78° C. for the free,crystalline ibuprofen corresponds to melting of the crystallinestructure. The complete lack of an endothermic event at the sametemperature for the MGCO3-IBU sample confirmed that the incorporatedibuprofen was not present in a crystalline state inside the pores. Nopeaks corresponding to any endo- or exothermic events could be detectedin the DSC scan between ˜35° C. to 150° C. for the MGCO3-IBU sample. TheXRD and DSC data shows that the magnesium carbonate according to theinvention suppresses crystallisation of the incorporated ibuprofen.

The dissolution profile of free ibuprofen and ibuprofen formulated withthe magnesium carbonate can be seen in FIG. 35. The dissolution rate ofthe amorphous ibuprofen formulated with the magnesium carbonateaccording to the present invention is more rapid compared to the freesubstance. The dissolution rate for the amorphous ibuprofen is aboutthree times faster during the first 5 minutes compared to the freesubstance and about 50% of the ibuprofen is dissolved and released fromthe carrier within 12 minutes while it takes about 30 minutes for thefree substance to dissolve to the same level. The apparent solubility ofthe amorphous ibuprofen formulated with the magnesium carbonateaccording to the present invention is higher compared to the freesubstance.

In the stability test, no signs of crystallisation of the ibuprofenformulated with the magnesium carbonate could be detected with XRD andDSC after that the sample had been stored at 75% RH for three months atroom temperature. Neither could any signs of crystallisation of theamorphous magnesium carbonate component in the formulation be detectedwhen exposed to the humid atmosphere.

As appreciated by the skilled person the drug Ibuprofen should beconsidered as a non-limiting example of the use of the magnesiumcarbonate according to the present invention as a pharmaceutical orcosmetical excipient in combination with an active substance. In thecase that the active substance is amorphous, crystallisation of thesubstance may be completely or partly suppressed by the magnesiumcarbonate leading to faster dissolution rate and/or increased solubilityof the substance. The magnesium carbonate of the present invention isnot only expected to act as a solubility enhancer when used as anexcipient but also as, e.g., a pH modifier, tablet and capsule diluent,adsorbent, anti-caking agent and free-flowing agent.

Example 29

The magnesium carbonate material was prepared as in as in the specificexample described above with the alteration that the first drying timewas reduced from 3 to 2 days. After 3 months of storage at 70 C thematerial was dried/calcined using a temperature of 300° C. The watersorption capacity of the calcined amorphous magnesium carbonateaccording to the invention was determined in the same way as describedin example 1 with references to FIG. 5. The result for the calcinedmaterial is illustrated in FIG. 36. The measurements shows that theamorphous magnesium carbonate according to the present invention aftercalcination adsorbs more than 0.6 mmol water/g material and even morethan 0.7 mmol water/g material at an RH of 3% at room temperature. At anRH of 10% at room temperature the calcined amorphous magnesium carbonateadsorbs more than 1.5 mmol water/g material and even more than 1.7 mmolwater/g material. At an RH of 90% at room temperature the calcinedamorphous magnesium carbonate adsorbs more than 15 mmol water/g materialand even more than 20 mmol water/g material.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described may be made without department from thespirit and scope of the invention as defined in the appended claims.

What is claimed is:
 1. A magnesium carbonate, wherein the magnesiumcarbonate is X-ray amorphous, and wherein the magnesium carbonate ischaracterized by a cumulative pore volume of pores with a diametersmaller than 10 nm of at least 0.018 cm³/g.
 2. The magnesium carbonateof claim 1, wherein the magnesium carbonate is characterized by acumulative pore volume of pores with a diameter smaller than 10 nm of atleast 0.8 cm³/g.
 3. The magnesium carbonate of claim 1, wherein themagnesium carbonate is characterized by a BET specific surface areaobtained from N₂ sorption isotherms of between 60 m²/g and 1500 m²/g. 4.The magnesium carbonate of claim 3, wherein the cumulative pore volumeof pores with a diameter smaller than 10 nm is between 0.018 cm³/g and3.0 cm³/g.
 5. The magnesium carbonate of claim 4, wherein the cumulativepore volume of pores with a diameter smaller than 10 nm is between 0.018cm³/g and 1.5 cm³/g.
 6. The magnesium carbonate of claim 3, wherein themagnesium carbonate is characterized by a BET specific surface areaobtained from N₂ sorption isotherms of between 240 m²/g and 1500 m²/g.7. The magnesium carbonate of claim 1, wherein the magnesium carbonateis characterized by adsorbing more than 0.3 mmol water/g material at anRH of 3% at room temperature.
 8. The magnesium carbonate of claim 7,wherein the magnesium carbonate is characterized by adsorbing more than14 mmol water/g material at an RH of 90% at room temperature.
 9. Adesiccant comprising the magnesium carbonate as in claim
 1. 10. A powderor a pellet or a film comprising the magnesium carbonate as in claim 1.11. An additive to a food, a chemical, a cosmetic or a pharmaceuticalcomprising the magnesium carbonate as in claim
 1. 12. An excipient in acosmetic or a pharmaceutical comprising the magnesium carbonate as inclaim
 1. 13. A method of controlling moisture content in a volume of amaterial, comprising exposing the volume to the magnesium carbonate asin claim
 1. 14. A method to produce magnesium carbonate, the methodcomprising: reacting MgO with alcohol in a CO₂ atmosphere, wherein thepressure is above atmospheric pressure, wherein the temperature isbetween 40° C. to a boiling temperature of the alcohol, wherein theproduced magnesium carbonate is X-ray amorphous, and wherein theproduced magnesium carbonate is characterized by a cumulative porevolume of pores with a diameter smaller than 10 nm of between 0.018cm³/g and 3.0 cm³/g.
 15. The method of claim 14, wherein the pressure is1 to 3 bar above atmospheric pressure.
 16. The method of claim 14,wherein the magnesium carbonate is characterized by a BET specificsurface area obtained from N₂ sorption isotherms of between 60 m²/g and1500 m²/g.
 17. A method to produce magnesium carbonate, the methodcomprising the steps of: mixing MgO and an alcohol-containing liquid ina reactor, to form at least one Mg-based intermediary that can interactwith CO₂; forming a carbonated intermediate product by reacting the atleast one Mg-based intermediary with CO₂, wherein the carbonatedintermediate is a liquid or a gel; and transforming the liquid or gelcarbonated intermediate product into magnesium carbonate by drying,wherein the magnesium carbonate is X-ray amorphous, and wherein themagnesium carbonate is characterized by a cumulative pore volume ofpores with a diameter smaller than 10 nm of at least 0.018 cm³/g,wherein the CO₂ that reacts with the at least one Mg-based intermediaryis at a pressure of 1 to 12 bar above atmospheric pressure, whereinmixing is performed at a temperature between 40° C. and a boilingtemperature of the alcohol-containing liquid, and wherein drying isperformed at a temperature below 350° C.
 18. The method of claim 17,wherein forming the carbonated intermediate product is performed at atemperature below 50° C.
 19. The method of claim 17, wherein thepressure is less than 5 bar above atmospheric pressure.
 20. The methodof claim 17, wherein drying is performed at a temperature between 60° C.and 300° C.
 21. The method of claim 17, wherein the cumulative porevolume of pores with a diameter smaller than 10 nm is between 0.018cm³/g and 3.0 cm³/g, and wherein the magnesium carbonate ischaracterized by a BET specific surface area obtained from N₂ sorptionisotherms of between 60 m²/g and 1500 m²/g.